Blue Cave of Xiji Islet

Xiji is an uninhabited basalt islet in the far south of Penghu, and on its side is a sea arch that small boats can enter when the water is calm. Light coming through the water and reflecting off the pale bottom fills the chamber with blue, the same effect as the better-known caves in the Mediterranean. Boats hold inside for a few minutes and back out. Whether the trip runs depends entirely on the swell.

What you actually see

• The blue light - sunlight through the water filling the chamber with colour.
• The sea arch - the basalt opening boats pass through into the cave.
• The islet cliffs - columnar basalt around the uninhabited island.
• The southern sea - clear water around the outer Penghu islands.

When to go

May to September is the season and calm mornings are when boats can enter. Any swell cancels the cave section of the trip. Winter is out of the question.

Honest expectations

Entry depends on the sea state and is cancelled often, even on trips that run. The stop lasts a few minutes. The blue is strongest around the middle of the day and weak in cloud.

Nearby

Dongji and Xiji are the outer southern islands, and Magong is north.