What cities is Europe are worth visiting, but only for two days?

I am going on a study abroad trip to Vienna, Prague, and London. While in london we have three weekends to travel. I am one of those people who like to stay in a place for a longer amount of time, so I can't think of any place I would like to stay for only two days. What cities are worth about 2 days of travel? I am more interested in Eastern Europe, but honestly, everywhere is great. My own ideas were Dublin, maybe somewhere in Scotland, Brussels, Munich or Amsterdam. I realize these are all Western, but I just want to stay longer in Eastern European cities.