To get to the Flayer Dungeon in Diablo 2: Resurrected, you’re probably going to have to hack your way through a lot of jungle until you find the Flayer Village where the Gidbinn is located. The entrance to the Flayer Dungeon is always close to the Gidbinn.
You need to get to the Flayer Dungeon in order to find Khalim’s Brain for the Khalim’s Will quest, but finding the Flayer Dungeon in the first place isn’t so easy. This is because it’s in the Flayer Jungle. And the Flayer Jungle, like all of the jungle areas in Act III, is large and very difficult to navigate. It’s very easy to spend a long time following completely the wrong path, or to end up in a different area altogether without even realising it.
Starting in the Spider Forest, explore until you find the Great Marsh. The Flayer Jungle is usually on the far side of the Great Marsh from the Spider Forest. Once you enter the Flayer Jungle, keep a constant eye on your mini-map. You’re looking for a semi-ruined village with a unique marker somewhere in the middle of it. The unique marker is a little blob with two horns coming out of the top and represents the altar on which Gidbinn can be found. Once you’ve found that, search nearby and you’ll find the stairs down to the Flayer Dungeon. Also keep an eye on the area name in the top-right corner of the screen. If it doesn’t say Flayer Jungle, then you’ve gone too far in the wrong direction, so turn back immediately.