Ragnarok / Valhalla Wiki
There is a Wikipedia article for this location.

River Gioll is a single map space in Midgard. It is connected to Nidavellir to the west and Slaeter's Sea to the south.

There is a lorkesth-infested river that cuts diagonally through the zone. Lorkesths are extremely dangerous to low- to mid-level players and should be avoided (though careful players may be able to farm them with ranged weapons for XP, since they are confined to the water).

On the east side of the map, miniboss Harbard guards a one-way staircase to Niflheim.

The zone contains no monsters other than those named above, and no random loot. Because of this, it makes a reasonable choice for playing with scrolls of wonder, wands of polymorph, drunken blessings, or other items that might have unpredictable effects, or be dangerous if interrupted by a random monster.