Q. What is it supposed to be on the show? A. An Internet Cafe. Q. Where is it supposed to be on the show? A. Somewhere in or near Miami. Q. When did we see it on the show? A. In Episode 10, of Season 6, "Ricochet Rabbit". Dexter has just exposed the fact that Professor Gellar is dead, and Travis is the real Doomsday Killer.  But Travis, in his insanity, is determined to carry on God's work (of ending the world). So, in this scene, we see Travis go to an Internet Cafe and access Gellar's blog. He looks at video profiles of several of the site's followers, looking for new disciples to help him continue the string of biblically-inspired murders. He finds someone who interests him: Steve Dorsey (AKA "Doomsday Adam"), an unemployed fanatic who seems more than willing to kill for the cause. (Travis later gores to Dorsey's house and recruits him and his wife into doing his dirty work.) Q. What is it actually in real life? A. The interior of a senior citizens center. Q. Where can I find it in real life? A. This scene was shot inside the Highland Park Senior Citizens Center, at 6152 N. Figueroa Street, in the Highland Park section of Los Angeles.

That's the same park where they filmed the scene of LaGuerta & Matthews talking in the parking lot.  And where they filmed the scene (in this episode) of Quinn waking up in his car.

Why?  Because the center is right next door to Travis's church / lair, which has been a central location all year.  So they found themselves filming a lot in that area.

Right around the corner from the church is the cougar's house.  And less than half a mile away, to the southwest are two other Season 6 locations: the barber shop (where Dexter killed the gang leader, Julio), and the fake coffee stand where Debra told Angel about her promotion.

Here is a Google StreetView of the center:

Q. How the heck did you figure out where it was?

A.  In previous seasons, I've usually had to hunt down the locations after viewing the episodes, using clues from the various scenes.  By the 6th season, though, I'd developed a small group of fans, spies & tipsters who kept an eye out for Dexter filming in their neighborhoods, and would let me know in advance when something was about to film there.

Between those reports, my own personal reconnaissance around town, and a few new resources I discovered, by the time the first episode aired, I already knew most (but not all) of the filming locations, and only needed to watch the episodes and match up the scenes with the correct locations.

This group of helpful fans includes Kerry, Rick, Ellen, Susan, Jason, Elaine, Joel, Julie, Geoff, Jeff, Jen, and others. My thanks to all of them.

Rick tipped me to this one, and I was able to verify it via another source.  It made perfect sense, since they also filmed in both of the center's two parking lots, and next door at the Abbey.