Mambo may be the most known museum in Bologna. It is a big museum, prices are not so high, and it is well organized. Very interesting collections exposed, especially temporary ones. Check their website http://www.mambo-bologna.org/en/ for updates.
Easy to take it all in in one visit. For visitors to Bologna that are art lovers, this is a great stop. The MAMbo is situated near an old river interesting site. There is also a nice Café which sometimes turns into a club and the museum shop is also worthwhile.
If you visit Mambo during June, check what's going on in the near park of Cavaticcio: free concerts, drinks, and food.
Tu-We: 12:00-18:00
Th-Su: 12:00-20:00