Yes there are lockers. Foreign tourist lockers you need to use the stairs for the high water slides. Locals are near the entrance. Tourist lockers are watched by a staff member for security.
Yes you have to pay a small amount I can’t remember specifics
Yes, for tourist its free, but rather small. You will need to take your own towel, as well I think. The lockers are a bit flimsy but they were fine, plus they are in a section away from every one else and there was an employee manning the area.
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