Källskär, located in the Åland archipelago, is a unique island known for its intriguing rock formations and the mystical "Källskär's grotto" or "sacristy," a naturally formed cave. Accessibility is primarily by boat, and tours are available from nearby islands like Kökar, as it is a remote location. While experienced solo travelers might explore independently with their own boat, guided tours are recommended for ease of access and to learn about the island's history and geology. Seasonal restrictions apply, with tours typically available during the warmer months (late spring to early autumn) due to weather conditions. A boat tour might cost around €50-€100 per person, depending on the tour operator and duration. A typical visit lasts from a few hours to a half-day, allowing ample time to explore the island's natural beauty and unique features. Note that facilities are very limited on the island, so it's best to bring your own supplies.