Loch Grynmear is really good all around. Recommend level 20 or so for full exploration. One difficult part of the quest there can be brute forced by being higher level, but you don't need to be if you pay attention.

Prison of Glymarach is fun if you don't mind losing some con. Level 35 or below only. Don't bother if you played the White Plume Mountain module.

Almost every area actually has some interesting hidden stuff and/or lore as well.

Sportsmanship killed CF