[Gallicus]

Ok, from memory:

First, as stated before, get the Helm of Serenity. Marten is useless to you until you have it.

As you enter the area, take a right and enter the cave. At the back is the hook & line - grab it. Then head back to the start and make a left turn (instead of the right which you just did). I have to type it this way since I forget the compass directions. Keep going (ignoring all caves) until you get the sledgehammer and plank. They're on the main way, so you can't really miss them.

From the plank, double back until you hit the first cave you see (it will be the second cave on the left from the start, if that helps more). Enter it and fall down one of the slippery slopes (you can't control movement). Head to a large main area, and here you can break a wall with the hammer. Behind the wall is a door which you can do nothing with. Ignore it for now. In the main section there is also a hole above. Toss the line up there (a rope will come down when successful). Head on up.

Once at the top, in the main room ajoining is a tough fight. Win and then head left. Loot the various skeletons on the ground until you get the spiked boots and tomb key. Then head back to the main room. Put the shoes any character (best on any character that can only use minimal armour, like a monk or mage, since it has 5 AC on them -- better than they will get in a very long time, if ever). Head down one of those slipperly slopes directly across. With the shoes, you wont fall. You will hit a crevise eventually. Put the plank there and cross.

Now, a door will be in front of you. Use the tomb key on it, and voila. The rest is up to you. You reached Marten.

*NOTE* This is purely from memory. I'm pretty sure its relatively accurate (I did it 3 days ago). There may be slight discontinuity with the order of events, but I believe it is enough to get ya by.