Rakutenchi is a small very busy local sento in a crowded Osaka neighborhood. The place was full of locals who all seemed to know each other as they chatted their way around the baths. The water was softened, and was piping hot in the main baths. The cold bath felt fresh. The small rotenburo filled with "Magma Onsen" treated water was small but nice. There's no view of the sky from the rotenburo as there's a panel blocking the way. The sauna looked small but clean and welcoming, no TV.
This is a good classic sento in a great location and one worth checking out, but this might not be the best sento for a first timer.

Magma Onsen is a common type of bath salt that is added to normal water just like you might do at home. It's probably the 2nd or 3rd most popular judging by how often I've seen it. The salts turn the water a reddish hue and has a mild fragrance to it.