My advice is definitively Berlin. In comparison to other big western European cities, everything is quite cheap (flight, transfer, transport, accommodation, food, drinks...).
You have lots of sights, mostly dry weather, and in case of volcano activities no problems to get back to Weeze by train/coach etc...
Second would be Hamburg, but what a pity no one flies there from NRN.
Other destinations I did like very much AND are reachable from Weeze: Budapest, Edinburgh, Cambridge, Bergamo
For more advices, maybe you can inform us about your main interests (e.g. sights/ museums/ shopping/ party/ history...)