In reply to phja:
Alps in spring is a bit of gamble. April is still alpine ski season. Even in May snowline can be at 2000 - 3000 meters altitude mark.
I would consider Norway if you like dramatic views.
Pico de Europa in my humble opinion is great, but it's much better to do as hut-to-hut or backpacking trip. Day hikes may not be that great because it's a long mountain range.
Had a very good walking trip to Mallorca in 2013. Loved it, but found locals to be a bit unfriendly with fences and restrictions everywhere.
Corsica is a gem if you want 5 - 15 days hut-to-hut. For day walks it's probably meh because exiting areas are quite deep in.
Maybe worth considering Cappadocia. It's very different to Alps or northern walking in Europe.
Iceland is reasonably good. Especially if you don't mind a bit of glaciers.