What does it mean?
Twll o le - a dump = not a very nice place, horrible, dirty, untidy and generally ych-a-fi.
Mewn gwirionedd mae Cardydd yn eithaf da! In reality, Cardiff is pretty good!
I'm guessing the course contributors are from Swansea!
The literal translation, "a hole of a place," sounds perfectly appropriate in some American dialects, maybe from Welsh, or more likely Irish, influence.