if i remember correctly, mainland theres a swamp full of zombies, bats and trees, and horrors. they are pretty easy.
Execution Grounds and/or Cruma Marshlands (both near Dion)? I wouldn't go there before level 25 with a non-twinked character.
Typical hunting grounds for that level would be the Ruins of Agony, Ruins of Despair and the area around Winmill Hill. From level 20 on, if you mostly care about XP, sign up for the winning side of Dusk/Dawn on your server and start going to the Necropolis of Sacrifice (you'll need a group, though, the mobs are 4xHP and all social to each other). If you like to make some nice money by the way, learn how to use the manor and start using it; Blue, Lute and Desert Coda should gain you nice rewards, especially from the mobs in the Necropolis.
hes probably talking about the swampland near de village. and yea, that'd probably be a good place for a non-twinked char to level, as would all the ones you listed - to the op, watch out for reds if you decide to level at windmill hill! :) gl to ya!