I have just spent two weeks in Istanbul scouring the city's historical monuments and unfortunately I found many sites throughout the city partially or completely closed for restoration. Much of this may not affect most visitors, but for those who like to know these things in advance I thought it might be useful to list all of these closures in a forum post for anyone's reference in the near future.
This information is based on the first half of May 2014. Contributions/updates by others are of course welcome.
The following are more or less in order of most to least important:
Aya Sofya (Hagia Sophia): Despite claims in the 2013 Lonely Planet that restorations had finally finished, there is major restoration work at the Aya Sofya. Inside, nearly half the nave under the main dome is closed and scaffolded on the north side. The upper galleries and mosaics are not affected. There is some scaffolding on the outside of the building as well, though not on the more visible southern side when I was there.
Topkapi Palace: Some annexes (e.g. the kitchens, the Chinese porcelain collection, etc) are still closed. The Ahmet III library in the Third Courtyard is now also closed and covered. You can also see what's closed/open by looking at the Topkapi museum's official site (topkapisarayi.gov.tr/en/visit-information). In the Harem, only one area is newly closed: the Valide Sultan (Queen Mother's) Courtyard. The Hünkar Sofasi (Sultan's Audience/Throne/Imperial Hall, a large domed room often pictured in guidebooks) and other areas were still off limits as they were when I visited in 2011.
Sultan Ahmet Tomb (near the Blue Mosque): Closed for restoration. The work appears to be due to finish in 2016.
Turkish and Islamic Arts Museum (Ibrahim Pasha Palace at the Hippodrome): Although restoration work was due to have been finished earlier this year, the museum was still closed when I visited and did not appear ready to re-open yet.
Archeology Museum: The main building, the "Archeology Museum" proper, is largely under restoration but the most interesting exhibits and collections are still on display inside, including "Istanbul Through the Ages", the Alexander Sarcophagus, and more. The Tiled Kiosk (Museum of Turkish Ceramics) and the Museum of the Ancient Orient were not affected.
Spice Bazaar and nearby: The Spice Bazaar or Egyptian Bazaar is undergoing restoration; it is still open for business but the exterior and the vaulted ceiling of the interior is mostly covered. The nearby Mausoleum of Valide Sultan Turhan Hatice (including the tombs of many sultans) is also closed and covered for restoration. These are next to the Yeni Camii (New Mosque), which is not currently affected.
Kariye Camii or Kariye Museum (Chora Church): A major restoration project appears to have begun. It will take place in 3 phases during each of which one third of the museum will be closed while the rest will be open to visitors. In May 2014 the nave (the largest area but also the least interesting as it has the fewest mosaics) was closed. If I understood correctly, the inner narthex (with possibly the most beautiful mosaics and domes) will be closed in the next phase and then the outer narthex and side chapel (including mosaics and frescoes) will be closed in the last phase (while the other sections should re-open). Presumably, this will occur over the next couple of years (see also a previous post: www.tripadvisor.com/ShowTopic-g293974-i368-k6815719-Restorations_at_Kariye_museum_Chora-Istanbul.html). The exterior of the building was also covered up. The narthexes and parecclesion are arguably the highlight, so until the end of 2014 you should still be able to see the best parts.
Süleymaniye mosque and complex: The mosque and most of the area is now cleared of restoration work. The northern medreses, the caravanserai/tabhane (travellers' inn) and the darüşşifa (hospital) were undergoing restoration but these were not previously open to visitors anyways.
More strangely, the cemetery and tombs of the Suleymaniye seem to be inconsistently open; despite a sign stating clear daily opening hours, I visited one time to find the cemetery closed for no apparent reason and another time to find the cemetery open but the mausoleums themselves (of Süleyman and his wife Roxelana/Hürrem Sultan) locked up. Rather disappointing and inexplicable.
Dolmabahçe Palace: Minor restoration work here and there inside the palace but nothing that stands out. The outer facade of one of the palace precinct's monumental gates (the northwestern one, opening directly on the main road) is covered up for restoration, but the one by which visitors enter is essentially identical and is unobstructed.
Naval Museum: The "old building" of the museum is closed for renovation, due to reopen apparently sometime in 2014. Currently on display are the museum's great collection of caïques (royal rowing boats) and an exhibit of Ottoman navy woodwork, and a few other things including a flag from the Battle of Lepanto and part of the Byzantine chain that closed the Golden Horn. Other collections (which you can see explore on the museum's website) are not on display, including the famous maps of Piri Reis.
Beyazit Camii (Beyazit or Bayezid II Mosque, near the Grand Bazaar): Closed and covered for restoration.
Nuruosmaniye Mosque: The courtyard and part of the surrounding complex is closed for restoration, but the prayer hall was open to visitors.
Zeyrek Camii (former Church of the Pantokrator): Still undergoing renovation, and could not be entered when I visited. At best, I suspect a restored section may open for prayers.
Mihrimah Sultan Mosque (at Edirnekapi, next to the land walls and not far from the Chora Church): Undergoing restoration. When I visited, the courtyard was closed but the great prayer hall was still open to visitors.
St Stephen of the Bulgars (Bulgarian Church made of cast iron, on the shore of the Golden Horn): closed and covered for restoration.
Yeni Valide Mosque and complex (Üsküdar): This complex is very visible when you get off the ferry at Üsküdar. It is closed and covered for restoration.
Nusretiye Mosque and complex (baroque-style mosque at Tophane): closed and covered for restoration.
Ortaköy Mosque (very familiar sight on the shore near the Bosphorus Bridge, often featured in pictures of Istanbul): this was covered for restoration, but some of the scaffolding appeared to have come down when I saw it again days later. I only saw it from the ferry so I can't confirm if was also closed inside.
Yoros Kalesi ("Byzantine Castle" at Anadolu Kavagi, at the end of the long Bosphorus ferry tour): Mostly off-limits for archeological excavations but part of the inner castle seems to open for visitors coming from the ferry. The view is better within the castle walls but still great even if you can't enter.
Eyüp: of less interest to non-religious visitors, but the tomb of Ayyub al-Ansari (Eyüp) itself is closed and under restoration. The mosque is still open and you get up to the doorway of the tomb, but no further.
Fatih Mosque and complex: the surrounding buildings of the complex (külliye) are undergoing restoration but the mosque itself and the tombs are open. The nearby baroque-style Mausoleum of Nakşidil Sultan is also closed and covered for restoration.
Fenari Isa Mosque (former Church of Constantine Lips): Appears to be closed for restoration.
Here are some other buildings that were affected by restoration but which are unlikely to be on most people's itineraries or to be of interest to them.
Other monuments near the Grand Bazaar and on Divan Yolu (the main street from Sultanahmet to Beyazit/Grand Bazaar):
- Koca Sinan Pasha complex is closed off for restoration.
- The Theodosius Cistern (Şerefiye Sarnıcı) is closed for restoration or excavations.
- The Mahmut Pasha Mosque is closed and covered for restoration.
- The Beyazit Medrese (Museum of Islamic Calligraphy) is closed for restoration.
- The Hasan Pasha Han and the Library of Ragip Pasha between Beyazit and Aksaray are being restored.
- The Ayazma Camii/Mosque is closed for restoration.
- The medrese section of the Şemsi Pasha Mosque (small mosque by Sinan on the shore) is under restoration but the mosque itself was open.
- The Atik Valide Sultan Mosque complex: the mosque itself is open but parts of the surrounding complex are closed or being restored, though these were likely closed to visitors previously anyways (some are in ruins).
Other buildings in Eyüp:
- The Sokullu Mehmet Pasha Medrese appears to be closed for restoration. The tomb may still open but I visited on Monday when most shrines are closed, so I cannot say either way.
- The Zal Mahmut Mosque is closed for restoration.
- Zeynep Sultan Mosque, near Gülhane, is under restoration.
- Molla Çelebi Mosque between Tophane and Dolmabahçe is closed for restoration.
- Çinili Hamam, near Zeyrek, is closed for restoration.
- Sokullu Mehmet Pasha Mosque at Azapkapi (in Galata) is closed for restoration.
- Bankalar Caddesi: some buildings, including what I think is the old Ottoman Bank building, is covered for restoration. Another old stone house in the streets nearby, possibly the old Genoese Podesta building or another nearby, was also closed and covered.
- The Botter House, a relatively famous Art Nouveau building on Istiklal Caddesi, was covered for restoration (or at least hopefully so, as it was reportedly in bad condition).
- Yavuz Selim Mosque complex: one of the less important tombs in the cemetery is closed for restoration.
- Küçük Mustafa Pasha Hamami: across from the Gül Camii, this is semi-ruined and now being restored.
- Sinan Pasha Camii (at Beşiktaş): The medrese adjoining the northeast side of the mosque is being restored, but the mosque is open. The courtyard and porch are slightly affected.
- Ivas Efendi Mosque next to the northern section of the land walls (close to the Prison of Anemas) is covered for restoration.
PS: I did not visit the Prison of Anemas to see if it was open to visitors. Last I heard it was being restored and converted to an art gallery. Also, the Tekfur Sarayi/Palace (Palace of the Porphyrogenitus), a Byzantine palace annex not far north of the Chora Church and part of the land walls, appears to be restored but inaccessible to the public when I visited (apparently to be used as a venue for conventions or special events, sadly); however much of it is still visible from outside.
If you have any questions about what I posted, or about something that I didn't mention here, feel free to send me a message or just reply here.