"Grexer"

A "Grexer" (n.) is a person who is to be found using the Grex computer conferencing system. These people are a friendly bunch who occasionally get together to do things that are fun.

You have stumbled onto the "Grexwalk" photo essays, which document one of those activities. You can join any Grexer activity without actually becoming a "Grexer". All you have to do is show up. You do run the risk of becoming an honorary Grexer, though.