Many Beijing guidebooks recommend going to a Chinese opera at the Liyuan Theatre. We don't. The show is a bit childish, and very different from our operas. Both the music and the production are of little interest, beyond the difficulty that must be involved in singing so high. In any event, if you're interested in going, the best thing to do is ask the hotel front desk to reserve tickets the day before. Tickets cost 200-480CNY, depending on available seats. Take a taxi from the hotel to the theatre (30CNY) o take the subway, Hepingmen station (line 2 circular) and walk down to the south. Here you have a map.
What we do recommend is having dinner in a Korean restaurant close to the Liyuan Theatre (no. 11 Nan Xinhuajie Street). Try the Hot Pots (stone-cooked meat), which are very popular with Chinese. Order the meat or fish that you like most (we recommend lamb and bacon) and grilled vegetables. The cost is around 100CNY per person.