What is the best/most affordable city in europe to travel to from Madrid?

I am studying in Madrid this semester and it is my first time in Europe. I am trying to decide what the best/most affordable city to travel to outside of spain. Everyone has opinions but I am looking for a good answer with good evidence!What is the best/most affordable city in europe to travel to from Madrid?Paris, very nice and easy by trainWhat is the best/most affordable city in europe to travel to from Madrid?Well Portugal the country it's self would be cheap by plane. If you go from Madrid, Spain to Lisbon, Portugal (it is gorgeous) for one night and one person it should be 34 dollars. But traveling by plane to cities closer is a lot cheaper. If you go to Dublin Ireland it will cost 70-150. Or you can get a Urail pass. You can by a pass to 21 countries, 3-5, 1 region or 1 country. And this you buy a pass for a length of time and all rail rodes are free to the threes to five, the 21 one countries you choose from a list, a region or one country. you can take a plane to one country and use the train system there. you may have to pay a reservation fee but that is no more than 15 USD. For one country and 15 days it can cost, For example Hungary for ten days it can cost 139 but you get to go everywhere in Hungary. Hope this helps