This is the first level of both Hexen II and the continent of Blackmarsh. It is an introductory hub, with several indoor areas with outdoors spanning a few places between them.
Bones of Loric
The first item to retrieve is the Bone Dust of Loric. This route will likely activate a Skull Wizard, which can be dangerous if you don't have a second weapon. If the wizard is too difficult, you can first enter the tunnel opposite the building, which has the second weapon visible once you reach the outdoor section.
When you start, you're already facing the temple you need to enter. On the right of a button that you can strike, which will open the secret door behind you. Jump in, and push the button next to the bars. Enter the teleporter to return to the surface.
Enter the tunnel opposite the building. This leads to a small room with archers in the corners, and one barrel containing a quartz flask. One pillar near the room entrance has a button, which turns the sacrophagus. Pressing the revealed button will then open the door. This door's tunnel will lead outside where you can get your second weapon.
For the bones, you will need to take the left tunnel. When you reach the bridge, drop into the water, and turn around. There should be a button on the wall which will open a teleporter. The monsters on the other side are somewhat prepared, thus you will need to kill them quickly or run past them.
With the bones, you can enter the Barbican for the Mill key, then head to the Mill for the bone dust.
Potion of Mithril Transmutation
In the laboratory before the Barbican, there is a gold pool. When you have the Bone dust of Loric, enter it and you will receive the Potion of Mithril Transmutation.
This item is used in the Barbican.