Legacy code names: Hard Climb, Cliff.
The traditional access route is underneath a cliff and the climb up is more difficult because you can get ambushed at the top.
An easy way to identify this fortress variant is that it looks like a circle/wheel on the map.
Visually: Circular fortress, No smoke stacks, no Detector Tower.
On the map: Perfect circle on the map.
Taking this climb up the back will take you to a high ground spot where you can destroy many of the fabricators in the fortress.
It was called hard climb because there is a nasty surprise waiting for you at the top of the mountain path.
A cannon turret and a bunker turret are guarding the way up.
You can bypass these by going left once you get up the mountain path, which will put you directly in front of two fabricators and at a high vantage point for the rest.
Strategy possible as of Patch 1.001.102.
Quite risky clear, although it doesn't take much longer than Crane or Bunker Hell since it requires about the same amount of repositioning.
I start at the bottom of the climb before moving up to sneak along the wall, making sure to dive whenever I am exposed.
I climb on top of the bunker turret and get the two fabricators in front of me with an Eagle 500kg Bomb before using my Commando to destroy the fabricators farther away.
I then hide behind the rubble and destroy the last two fabricators with my other Eagle 500kg Bomb.
Uses Eagle 500kg Bomb, Orbital Precision Strike and Commando.
Risky and impractical, but goddamn does it look cool.
Hard to see in the video but while I use my Jump Pack from the fortress I call an Orbital Precision Strike and throw it on the last 2 fabricators.
In Canis' video she uses a second Eagle 500kg Bomb but I use an Orbital Precision Strike so I can use the Jump Pack out of the base 2 seconds faster.
This one takes a lot of practice but if you can pull this off then props to you.
Approximate time to clear: 45s
This is an example of a non speedrunner solo clear.