Board a tiny boat for a forty-minute float through neon-lit limestone tunnels and mirror-like subterranean lakes. It stays a steady 18°C inside, so bring a light layer even in mid-July. The Vlychada cave is the one to book; skip the dry sections if you're short on time. Arrive right at opening to avoid the tour bus swarm. The water is 30 meters deep in spots, so keep your phone gripped tight for those reflection shots.
