Pansol is the strip along the national highway between Calamba and Los Baños where dozens of pribado (private) hot-spring resorts cluster wall to wall. You rent a complete walled compound — pool, pavilion, kitchen, sometimes a small house — by the hour or by the day, typically for a few thousand pesos for a family-sized place.
Quality varies. The cheaper places are concrete tanks and plastic chairs; the better ones (sometimes called exclusive resorts) have landscaping, slides, and clean changing rooms. Weekends are crowded, especially with Manila day-trippers; weekdays you can have a whole resort to yourself. Bargain on the rate, and check the water before you book — some pools run hot to the point of being uncomfortable.