Mount Athos, the third and easternmost of Halkidiki's peninsulas, has functioned as a self-governing monastic community for over a thousand years and remains off-limits to almost all visitors — its two-thousand monks and twenty monasteries are best seen from the water.
Since women (and, in practice, most independent travelers) cannot set foot on the Holy Mountain, a boat cruise along its coastline from Ouranoupoli is how the vast majority of visitors experience Athos. Cruises pass close enough to see the cliffside monasteries — Simonopetra's tiered wooden balconies stacked against a sheer rock face are the most striking — while a recorded commentary explains each community's history.
This 14th-century Byzantine tower standing right on Ouranoupoli's waterfront once marked the administrative border of the Athonite monastic state and now houses a small folklore museum. Climbing its narrow stone stairs gives a good vantage point over the harbor where the Athos cruise boats depart.