Here is my guide to all three footbaths which are super necessary for a lot of achievements, and 100%ing the game.
1. First bath is at the top of the elevator that starts down by the yacht.
2. Bring 5 blood crystals, and you'll get double jump.
3. The second is along that pathway that goes from the apartments to the cargo waterfront area/fields.
4. It'll be up off the path, you can also see it from the very top of the barracks. Bring 5 blood crystals for double jump.
5. This last one I struggled with, not sure why. It's next to the two tall apartment buildings.
6. Bring 5 blood crystals, and you'll get sprint in mid air.
Hard to describe - the video is much more clear. Good luck!