"Cross-country skiing is fun!"
Translation:Hiihto on hauskaa!
You're right but we usually say just hiihto when we mean cross-country skiing and laskettelu for downhill skiing.
I generally agree, but also find that this a changed a bit over the years. 30 years ago I could be sure that someone meant cross country when they said hiihtää, but now... not so much.
To Luke: Cross country skiing is called maastohiihto or murtomaahiihto in Finnish. They sound very formal, though! People often shorten murtomaahiihto just to murtsikka.