Naberius is a necromancer that is found in the Old Cave in Broken Valley near the Chapel Shrine. It's not the Lost Cavern directly next to it, but can be found further west. Naberius lets you start the quest Vigor Mortis .
You can mind read him for 120 exp to learn the password to his storage that is located in a portal from outside his cave, however, to get through the portal you must acquire the password which is Bellegar. To find the password you must find all four parchments each containing a single word in Draconian, which can be translated for you by ZixZax near the Maxos Temple.
Once inside the storage main door, there is another door that cannot be opened without a key, which is dangling from the hand of a skeleton to the left. Taking the key spawns 3 level-14 skeletons.
His storage contains a Skill Book as well as some gems, the Blood Echelon Shield, and some random items.
You can also jump up to gain access to the area of the storage which is behind the ruined chapel, be aware once inside three lvl 14 skeletons await when you pick up the key as well as some foes along the way. After reaching Talana your jump is improved so then its another option to get to the storage.