Unmissable architecture and scenery. Catch a ballet if you can, very high quality, we watched Cinderella. The layout of the audiotorium is very cleverly designed so acoustics and visibility are optimal wherever you are sat. Reasonably priced tickets

Visited the Opera House in Oslo and had an outstanding uniquely norwegian lunch at their cafe/restaurant on the main floor overlooking the fjord. The best meal we had in Oslo!

Architectural marvel. You can even walk on the roof

A really nice piece of modern architecture in Oslo. Didn't go in, but in fact you don't even have to - you can climb all over the building rising very high above the building's neighborhood and enjoying good views of the surroundings. Good for picture-taking and just lounging on the marble facade plates in good weather.

Wife and I went and saw the Nutcracker there. Beautiful building, great acoustics.

I did not see the inside of the Opera House, but instead went onto the roof late at night. It is 'open' all the time, and has architecturally interesting slopes (and stairs!) where you can see over the centre of Oslo. The views at night are beautiful and peaceful. I highly recommend it!

Very special architecture, worth the visit, like an iceberg in the water.

increddible pice of modern architecture near the central rail way station in Oslo.

You can't really miss it unless you avoid this part of the city somehow (not likely). I highly recommend a visit to the opera house to walk around and on it. One of many highlights for this wonderful city.