The Pension Gehrig guesthouse is located near the Paradeplatz where most of the local trams pass through. This makes it a perfect location to visit all sights of Mannheim. Also the Castle of Mannheim is only a short footwalk away. All you need is located nearby, like a supermarket, restaurants and the shopping mile. The entrance is hiding behind the patio of an an italian restaurant.
The room I had was a twin bed room. There are only 6 rooms altogether. It was clean but I found two long black hairs in my bed, although the linen was new. The bed itself wasn't too uncomfortable bit a little too hard for my low weigh but is sufficient for a weekend stay. The room also comprised of a fridge, a sink with a mirrored cabinet, a wardrobe, a table with two chairs and a small tv. Altogether the room was basic but you won't expect more from a 28 EUR room.
The sanitary installations (all on the same floor) comprise of two separately lockable baths with shower, mirror and sink. There are also two separate toilets nearby. All of it was very clean.
In sum the Gehrig guesthouse is recommendable of you want a cheap and clean stay directly in the heart of Mannheim. The rooms may be basic but with 28 EUR for one person or 45 EUR for two its rates are very low.
Personal recommendation: get to see the Wasserturm and also the great Luisenpark! If you visit some locations check if you might want the Mannheimcard with gives you many rebates and free use of the trams in Mannheim.