Heidelberg, Germany:

Settled In: Celts camped here as early as 400BC; Romans in 1st Century; first permanent fortifications 1000 AD.
Officially Founded: Founded in 1050 AD, Free Imperial City in 1219 AD, joined Bavaria in 1806.
Language: German, but basic English gets you by.
Suggested Stay: 2-3 Full Days with overnight stays.