Has anyone ever successfully either mapped or navigated these things? Every walkthrough I've read mentioned 3 keys in the first three barrows you enter. There was none in either of the first two, and the third is destroyed whenever you use it. Any suggestions on how I can complete the quests in here?

This quest was always a pain because I had lost my notes from the last time I went through (and I've also lost them now :p ). All the keys are in there though. Write down all the thombs (and the tombs they lead to) to make sure you visit them all.

Just walk around the tombs as much as you can. I think it's a fun place to wander about :D

But I don't really think there's a map, I myself just bump around all over the tombs...

It is quite easy to map - when standing before the exits (or entrances) - you have there either the number of the barrow to what the entrance leads, or tree (outside) or something other (the special quest barrow). So, just write down something like :

Barow No Exit 1 Exit2

xxx a b

P.S. Note, that some of the connections are one-way.

P.S.2. I think that the quest items are generated only when you have accepted the respective quest. So I had to return there, when looking for the damn Lantern of light (or what was the name).

You need the keys to open up the rocks which reveal the maps, which I have never been able to find. I guess I could do a trial and error type thing, but that can be a pain in the butt since my party is level 8 (or so).