Otherworldly things have been going on at the Underground Tour of Seattle. A crew filming for The Learning Channel (TLC) showed up Tuesday night to film 12 people spending the night in the Underground.

Their mission: Search for ghosts.

The overnighters were recruited from A.G.H.O.S.T., amateur ghost hunters of Seattle and Tacoma. Los Angeles producer Michael Brockhoff picked the group because they use a computer search system.

Brockhoff wouldn't say whether the hunters, who chased ghosts from 9 p.m. Tuesday to 2:30 a.m. Wednesday, had spotted any spirits. He teases, "Wait and find out." (The segment airs as part of TLC's "Mysterious Worlds" series this fall.)

Underground Tour owner Sunny Speidel reports, "I talked to some who said they'd seen low orbs of light and recorded them digitally. They left assorted letters on a Scrabble board. When they came back, three letters were placed elsewhere. The letters spelled 'CAT.' "