St. Olms Underworks is part of the Vivec, St. Olms Canton.
The husband of Moroni Uvelas, Danar, is a Skooma addict who spends most of his time in the Underworks using Skooma. He has been missing for some days, and his wife fears he cas contracted Corprus, thus asking the Nerevarine to look for him and cure him, if possible. They find a Corprus Stalker down in the Underworks, that once was Danar Uvelas.
One of Caius Cosades' informants concerning the Sixth House can be found here. Her name is Addhiranirr, and she is a Khajiit (Morrowind) who is also a member of the Thieves Guild. She is hiding in the Underworks so as to avoid a taxman looking for her.