Andorra - Pyrenees
At around 2000-2500m, the perfect altitude for red blood cell gains. Popular with the pros not only for low tax but also to 'sleep high', belt down the valley and 'train low'.
Andorra is a beautiful country with incredible mountain scenery, wonderful food and hotels.
However the roads are busier than in the surrounding countryside, and they will require that you bring your mountain legs.
Take care as EU SIM cards won't work here, so you can rack up an expensive phone bill if you are not careful!