It's called MuMart and is the first institutional museum of contemporary art on the seabed.

On display are installations by 14 contemporary artists of international renown.

How can you visit a sunken museum?

Through guided excursions on the Mizar, a semi-submersible, but if you prefer also snorkeling

 

(http://www.lanuovasardegna.it/olbia/cronaca/2017/08/08/news/golfo-aranci-il-museo-sottomarino- ago-the-full-of-visitors-1.15709826)