First of all, file this one under«hole in the wall». Of course, in my experience you find the best music in places that care more about the quality of musicianship than décor. The Den does not disappoint. The quality of music is excellent(think classic 70 – 90’s rock). The place is clean in a gritty-no-nonsense-we-had-PBR-on-tap-before-it-was-ironic kind of way, but comfortable and low key. The clientele is blue collar and 30s-50s. If you are looking for music in Mansfield this is your best call. BTW it is hidden behind subway.