Throughout the day, boats leave from Passeig de Ses Fonts. They take you to Cala Bassa, a sandy beach on a thin strip, for 6€ one-way, or to Cala Conta, a slightly rocky beach, for 6€ one-way. If you negotiate, they will take you along the coastline northwest to the far point of Portinatx. This is virtually the only way to see the coastline, since there isn't a road running along it; most visitors agree it's Ibiza's most beautiful coastline.
North of the waterfront, the chief attraction is Sa Cova de Santa Agnès, a national monument and an object of eerie devotion. This has been a place of sacred worship ever since a sailor prayed to Santa Agnès during a rough storm and was saved. The sailor, to show his gratitude, placed a figure of the saint in this dark hole. It's become a place of pilgrimage ever since. You may view it free on Monday and again on Saturday from 9am to noon.
If you have rented a car, you can explore Cueva de Ses Fontanelles, north of Platja Calad Salada, where faintly colorful prehistoric paintings decorate the walls.
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.