1 - Starting Point
2 - Liam's Workshop
There are two things to loot inside: the chest at the foot of the bed (for a magickal trap and a scroll of disperse magick) and the dresser beside the bed (for Liam Cameron's Journal). The journal tells of a portal that has been releasing strange creatures into the area, and Liam's attempt to destroy it. Hang onto the journal so you can return it to Mrs. Cameron.
3 - Path
Follow the path away from Liam's Workshop. You'll have to fight some void creatures along the way, but eventually you'll stumble upon Liam's body. You'll find another magickal trap if you loot it. So obviously Liam didn't close the portal.
West of Liam's body you'll find the portal. If you had an easy time with the void creatures along the path, then you might want to hang around the portal for a while killing void creatures (the portal will keep producing them).
When you want to destroy the portal, there are two ways to do it. If you have a technological aptitude then you should use the magickal trap. Otherwise, you should use the scroll of disperse magick. Just put the appropriate item into one of your quick item slots, select the slot, and then target the portal. Destroying the portal also kills all the void creatures nearby, so if the void creatures are tough for you, you can just run past them.
Destroying the portal nets you about 4000 experience (if there's a full set of void creatures nearby) and adds to your alignment.