Yes, its a hole.
Once you arrive at the hole, you'll find that its really nothing special... yet. If your active pet has a petpet attached, it will do one of the following: [petpet name] shakes nervously, spins in circles, chirps, shudders with fear, or loos into the hole curiously. If your active pet doesn't have a petpet attached, switch to one that does or attach one.
Once you've got your petpet there, you have five options to basically get your pet into the hole. Climb in slowly, Dive in with eyes open, Dive in with eyes closed, CANNONBALL!, or BELLYFLOP! Note that whichever option you choose has no impact on the results.
Once you've jumped into the hole, your petpet will jump back out a few seconds later and almost always, nothing will happen.
However, sometimes something does happen! You can either win an item, a couple neopoints, your petpet will gain age by a few hours or sometimes your petpet's level will be raised.
My friend told me I could choose what I win!
Well, your friend is wrong. But before you go and punch them in the face, you can see what it would look like if you did win whatever prize you wanted. Just change the &e=0 part of the URL from 1 to 7.http://www.neopets.com/medieval/symolhole.phtml?type=end&e=0&rnd=483734
The following items can only be obtained from the Symol Hole.
Getting the avatar is completely random, but it may be easier to get on Groundhog Day, February 2nd (This has not been proven).
Next sleep in 0h, 17m, 51s.
Jul 31: 9 AM/PM NST
Aug 1: 8 AM/PM NST
Aug 2: 1 AM/PM NST
Aug 3: 6 AM/PM NST