Skim across the sea from Kos to spend a day on the volcanic shores of Nisyros. Descend into the vast caldera at the heart of the island, and then while away a free afternoon in the port town of Mandraki, where you can grab lunch, visit the monastery, or soak in geothermal hot springs.

Get picked up from your hotel and head to the pier, where you board a boat to cruise over to the neighboring island of Nisyros. When you arrive, make your way to the volcanic valley, which, at 2.5 miles (4 km) across, is the largest in Europe. If you'd like, buy a ticket to venture down to the center of the caldera and see the shimmering yellow crystals formed by the sulfurous steam venting from the earth.

After visiting the volcano (optional with extra charge), enjoy 3 hours or so of free time in the charming, whitewashed village of Mandraki. Find a quaint taverna for a bite to eat, and consider making the 128-step climb up to the Monastery of Panagia Spyliani, the perfect vantage point for gazing out over the azure waters and Nisyros' surrounding islands. If you'd like, you can even visit the renowned hot springs on the outskirts of town, relaxing with a therapeutic soak amid the pistachio, olive, fig, and almond trees before catching the boat back to Kos.