Heading to Berlin for a weekend in May - and there will be 3 of us. 1 guy, 2 girls, in our 20s/30s. We do want to do some of the standard sightseeing - but also want a place with a fun night vibe. We're NYers, so walking is not a concern - but we do want a fairly central location. We'll likely check out an apartment rental through airbnb.com. Any suggestions?! Thanks!