The instance can be found at the foot of the Barrow. You can enter only in a group, even if you are alone in it. Instance lives 12 hours, trip can be repeated every 3 days.

If you leave party or party is disbanded - you automatically teleport to the foot of the barrow.

This instance is unique because its map changes every time you enter. The only thing that is solid and constant is the following:

B X-X
A - A
-. -. -
A -. -
......E

E = entrance.
A = arboris fungus (level 9. you can get shizka mushrooms from it, if you have the guide learned. The closer you are to level 9 from the upper side - the higher is your chance of getting them.)
B - Bog Elf
X - Location does not exist.
1 of the "-" locations will not exist and randomly floats around the map. You can get around it.
Every location has a tussock. when clicking on it you can find either nothing, or one of the following: 1 efril, 15 s, 10 s, Weetsa, Bottle, Pile of Papers, Rare scrolls of poisoning/healing, Ratgikon leather/bubbly metal. Once again, the location in which you would find the one that has the treasure is not constant.

Mobs.
You will find:

Caustic Kakurt: Uses toxic bite (same aspoisoned steeds), unlimited number of times, pretty often. your best bet is kill it as fast as you can. You can not remove the bite using antidote. 1492 HP

Caustic Phitzell: Uses toxic bite (same aspoisoned steeds), unlimited number of times, pretty often. your best bet is kill it as fast as you can. You can not remove the bite using antidote. 1603 HP. Drops higher green pauldrons.

Last but not least, good old arboris fungus, but now level 9, 1342 hp. mushrooms drop to everyone in the group that was in the fight and has the guide learned, but you could also get unnecessary shrooms.

Bog Elf.

9202 HP.

Strong mob by itself, but also uses some magic:

Poisonous Reed - All the HP you deal on him comes back at you. Both magic and physical. Can be removed with charm dispersal scroll found at the undead hunters shop.

Power of the Heart  - uses twice - around 50% hp and 5% hp. if not removed with the antimagic scroll - heals Bog Elf full HP.

Tips and Tricks:

1. Once again, do not hit in block. If he uses magic on you - it will be critical cast every time.
2. Everyone in a party should have charm dispersals
3. At least one person has to have antimagic scrolls
4. If you die - he will call a lot of mobs to his side, even if you cleared the location before fight.
5. From 4, clear location at first. you do not want to be fighting kakurts and phitzels that bite when against this guy.
6. Sometimes he calls level 5 kakurts to his side. Not too strong, but they also bite quite often.

Drops: swamp heart flower if you learned the guide, chance of relict fossil.