With Himmelbjerget (147 m high) as its highest point, I doubt we'll find many valleys in Denmark :-)
Actually, the highest natural point in Denmark is Møllehøj at 170m, the actual highest point is the top of Østbroen over the Storebælt connecting Fyn and Sjælland, which has its pylons at 254m high. Which, when your highest point in the country is a bridge pylon, you know your country is flat
Absolutely (it practically is the same word), though I think "dale" is relatively uncommon in contemporary English. The only uses I can think of off the top of my head are in "The Army Goes Rolling Along" and maybe "The Farmer in the Dell."