Bloodstalkers can fit through the entire length of the cave and can easily get past the underwater part, as well as dispatching Arthros from a distance, arguably the best mount for the cave. (Note there seems to be a glitch where if you die while riding a Dino, that Dino will fall through the map)
This table is incomplete.
You can help us by adding the tamed creatures you know can enter the cave. If the creature can't enter, please exclude it.
Leeches are in this cave so bring the materials to make a fire.
There is a part of the cave where even a Raptor/Deinonychus cannot fit that is about halfway through the cave; However a Deinonychus can scale the wall of the cliff/ledge just before the Artifact of the strong and still access that part of the cave. Fully Traversable with a Deinonychus.
The entrance is at the bottom of the northern end of the spider trench.
The Broodmother spawns outside of the cave itself in the ramp area down to the cave. You can go around her with a Deinonychus by going straight through to the cave, or drop into the trench at the cave entrance.
She also takes more damage and deals less damage than the Arena and Island boss versions of the broodmother. Damage taken is somewhere around 3-4x.
Health of the Wild Broodmother at level 20 was 578,000. At level 77, 1,166,400. So bring plenty of damage!
Strategy to kill can be shooting down from the nearby cliff edges with either a shotgun or other weapons as you deal approx 4x damage. You could also bring four Rexes and use a cryopod to hold them as you go into the cave.