Make sure you try currywurst in Germany. It's basically a hot dog with tomato sauce (ketchup) and curry powder. Tastes brilliant and only costs 1 or 2 Euro.
I went alone last summer (06). I met some wonderful people…I liked it so much, that I am going on the London + Paris trip next week (alone again).
Definitely worth doing if you are in any way interested in Ancient Rome - the guide is a wealth of knowledge.