The pain cave is a nasty place where there is only one person on your shoulder......the one telling you to stop. make the pain go away, slow down. The other angel that tells you to keep working, that your almost there, got frightened by the cold inhospitality of the pain cave and has long since left for orlando or tampa. Some peoples caves are sharp, nasty, and dark, others seem to have cushy furniture and carpet with air conditioners and foot rests, everyones is different.
I found this picture on smithersmpls blog (he is a roadie and has a funny blog).
he also incorporates the "hurt locker" which typically resides inside the pian cave. more on this later.