I'm a level 64 Nord and am trying to level to 70 to get achievement Legendary dragon. Having completed all quests I am revisiting various sites in an attempt to level up. I fast traveled to Yaphet's Folly and now cannot leave. You cannot fast travel away or swim away. Autosave overwrote my previous save where I traveled to Yaphet's Folly. I don't want to create a new character since I have months invested. Any ideas or suggestions?
I hope you're on PC and not a console, because if you're not, you're probably screwed.

From the Wiki -
Under no circumstances should you fast travel to Japhet's Folly by yourself and not following the quest. Japhet's Folly is its own "world" in the game and once you are there you cannot fast travel or leave in any way other than ending the quest with Adelaisa, who won't be there if you fast travel there on your own. (You can't leave no matter what you do. Exception: you can still get kidnapped by Astrid.)
That "exception" is obviously a
very narrow window, for reasons I can't go into here because doing so would count as a spoiler.
If you are on PC, you can use the
player.moveto command to get out.
If you happened to fast travel to Japhet's Folly and cannot escape by the normal means, you can use the http://www.uesp.net/wiki/Skyrim:Console#moveto console command to place yourself on the normal skyrim realm. Example: player.moveto 00019DDF plops you right outside Riften, consequence free..
The
coc command will work too.
You really need to be maintaining a number of saves any time you play one of these games. Now you know why.