Q:What is "Deep 13"? (answer provided by www.mst3kinfo.com)
A: It's a cavernous underground lair, located deep in the sub-basement of Gizmonic Institute (13 levels below ground level, hence the name), near the Institute's atomic pile, where Dr. F. and TV's Frank lived.
Q:And just who are Dr. F. and TV's Frank?
A: Why, they were the evil scientists who imprisoned Joel and then Mike and forced them (along with their robot pals) to watch horrendous movies.
Q: Can I watch these horrendous movies?
A: Yes! You just need to watch Mystery Science Theater 3000 (or MST3K for short). See the above link for more info than you can shake a robot at.
Now, everybody sing along:
"In the not-too-distant future
Way down in Deep 13,
Dr. Forrester and TV's Frank
Were hatching an Evil Scheme."