Hub 5: Vivarium

Vivarium is a bonus level in Hub 5: Necropolis in Hexen.

Walkthrough
This level is optional, but it will provide lots of helpful items for the final hub. As the intro suggests, the entrance portal is only available before you enter any of the tombs, after which it is closed off.

There are face-like walls that shoot Porkalator charges at you, among other unpleasant things. Let one of those charges hit you, then, in your pig form, run through the small passage near the starting point. It leads to a secret room with a lot of goodies. Then wait until you're human again, pick up everything you can and open the huge door leading out. Alternately, if you are the Cleric and have the Wraithverge, you can fire it at some enemies near the south wall, and one of the weapon's ghosts may activate the shootable linedef on the other side, granting you access.

To get back to the hub, use a weapon on one of the linedefs to either side of the middle hexagon at the north side of the map to lower a lift.

Variations
Depending on which character class you play as, different enemies appear in the level. As the Fighter, there will be Centaurs, Slaughtaurs, and Green Chaos Serpents. As the Cleric, you will face Dark Bishops, Brown Chaos Serpents, and Ettins. As the Mage, there will be Reivers, Afrits, and notably Wendigos, who otherwise only appear in the first hub. While there are always Ettins present, there are more for the Cleric.