1. San Alfonso del Mar – Algarrobo, Chile
Stretching over 3,300 feet along the Chilean coastline and covering 20 acres, this man-made lagoon is practically an inland sea. With a capacity of over 66 million gallons, it’s even navigable by small boats and kayaks. You can swim, sail, and even scuba dive—all in water pumped directly from the Pacific Ocean and filtered to Caribbean-blue perfection. It’s the crown jewel of mega pools.