So you have no recent saves or an auto-save before this?
There is a path that winds back and forth up the mountain, with a teleporter shrine near the top. I assume the problem you are having is getting through the level 18 opponents.
Drop the game difficulty, if you are not already playing on easy (you can always raise it again when you get out of your current predicament).
What class are you playing?
Do you have your creature yet? The demon or ghost summon may also help, if you have them or any spare skill points to try them out (make a new save first).
Hit and run tactics with a bow might help, especially if you landed somewhere where you can get in range of the goblins without them being able to get to you. I don't recall any places like that, though.
If you have enough potions and a fair bit of luck you might be able to run through groups to get past them.
At level 15 I went to the fjords and got up to 16 with the first couple opponents. Reaching the bottom of the path brought me up to level 17 (I cleared the next beach and swam over to another to get up to level 18 before heading to sentinel island).
On level 16 I didn't have too much trouble, but then I always had an area clear behind me I could retreat to if needed. Being 2 levels lower would make things noticeably harder (though not necessarily impossible), and you may not have a safe place to retreat to until you clear out the first group.
