The Underground River
but now i'm watching Made in Abyss and oh man it's probably like...my second-favorite anime ever now. Gurren Lagann is the only thing above it. Made in Abyss is basically everything i like in a setting and story. exploring a strange setting that only gets stranger the further you go. actual danger for the characters. a beautiful soundtrack and world design. fantasy, but not the generic medieval fantasy - it's got steampunk influences, but it's not entirely steampunk. a very cute fuzzy animal girl i want to hug.
oh it also gets very uncomfortable to watch. in a good way, i guess. it's very rare for media to make me physically wince when something happens to a character, but MiA does that and does it well. episode 10 has one of the most viscerally painful scenes i have seen in an anime so far. and after reading the manga, i know what'll happen in the finale...and it's gonna be even worse.
go watch it. if you don't plan on watching it, at least listen to some of the gorgeous background music.
(also bondrewd is a horrible, horrible man and stole shou tucker's #1 dad trophy. well. in the manga at least. we won't see bondrewd be a dad in the anime...)