My niece (16) will be coming to visit at the end of the summer and I'm looking for places I can point her to so she can have some fun with folks her own age. While I'm definitely the cool uncle, I want to find a balance between her having a good, memorable time but also not getting too wild. I'm also aware that certain places/events don't allow under 18s.

She likes music and is pretty artsy all-around - theater is big for her, painting, fashion. Nothing too sporty or outdoorsy.

Anyone have any suggestions of cool hangout spots, events in late August, things like this?

*Edit: To clarify, I've lived in Prague for a lot of years, but only as a (childless) adult, so I don't need more general recommendations. I'm looking for anything like clubs, concerts, youth-oriented cafes, very short-term camps, etc. that very specifically cater to the like 15-18 /- crowd.