I did a search and I couldn't find anything about this.
This trick requires a Traveller's Tundra Mammoth/Grand Black War Mammoth/Grand Ice Mammoth.
I was testing out exploration locations in IF when I stumbled upon this.
Firstly you'll have to stand right next to this pillar so your character won't move anymore.
Next, mount up on your mammoth and it should look like this (if you have a priest friend, get him to cast levitate on you so you take 1 step shorter to get up) then logout.
If you didn't have a levitate cast on you, you should look like this after logging back in. If you've done this correctly you should beable to mount your mammoth again without falling down. Logout again.
After you get on top of this ledge, you can move to the left window and step up, then mount up and log off again.
and here's the final result
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