Anime [12 Episodes] | OVA [1 Episode]
This single episode OVA is based around everyone going to the hot springs. It's a good chance to relax, but knowing the characters, it'll be more chaotic then relaxing. The episode is actually more entertaining then the entire series and has more memorable moments. If I remember correctly, every character in the entire series that maters is involved, so it's best you watch it after finishing the series.