Nexus

"The Nexus is a mysterious place that is connected to dozens of places all over Vallaris. It exists at all those places at the same time, or something, and it is a really handy way to get around. Or it used to be, anyway. I think its broken, just like everything else around here." - Merchant

Forge
The Forge is used to acquire certain weapons that aren't found in chests, and it requires ore in order to craft them. At first, the forge is unlit and cannot be used. Once you rescue the Merchant in the Shattered Rift, he will light it up so you can use it. The Weapons that can be crafted in the Forge are limited to the forge level.

Trading Shop
You can trade soul shards with the Merchant in order to get certain trinkets that aren't found in chests.

[Insert name of the prison of Alyssa and King Valor]
This entrance to this prison is also within the Nexus, underneath the surface.