Siaes Tunnel is a boat-access advanced dive on the northwest side of Ulong Island, usually reached in a 30 to 45 minute speedboat run from Koror. The site is a large overhead cavern with multiple reef-wall openings, so the plan is a deliberate guide-led descent rather than a casual reef drift. Light, black coral, reef sharks, and stingrays make it a standout Palau tunnel dive.