Skip the heat stroke and hit the site at 8am before the tour buses descend. You pay extra to swim in the Antique Pool, but floating over submerged Roman columns is the only way to tolerate the humidity. Hike up to the amphitheater for the view, but ignore the half-hearted museum near the entrance. Spend three hours tops, bring a massive water bottle, and wear shoes with actual grip for the uneven marble ruins.
