Cape Verde
For two hours around midday, sunlight sets a submerged lava cave burning electric blue.
You lean over black basalt and look down a shaft in the rock. Around noon the sun finds its angle and the seawater at the bottom ignites into a ring of blue so saturated it seems glowing from within; miss the window and it is just a dark hole breathing sea air.
Buracona is a stretch of lava coast on Sal's north-west shore where the Atlantic has hollowed caves and pools out of the basalt. Its Blue Eye is an underwater cavity that catches direct sun in the late morning; the physics is plain, red light absorbed, blue intensified, and the result looks anything but. A local community association manages the site with paid entry and guides, and the Eye itself is for looking rather than swimming; a separate open volcanic tide pool provides the dip, calm and clear behind the wave-battered outer rock. Come in closed shoes, carry water for the shadeless ground, and expect company at the peak window.
Solo
Arrive when the site opens, walk the lava shelf while it is quiet, and let the Eye's midday window come to you.
Couple
Catch the blue at its peak, then save the tide pool for the afternoon once the excursion buses roll on.
Family
Children love the moment the colour switches on; keep them in sturdy shoes on the sharp basalt and swim only in the designated pool.
Friends
Fold it into an island loop: the Eye at noon, a shared dip in the lava pool, lunch back along the coast.
Nothing is served on the basalt itself; carry water for a site with no shade.
Plan lunch back along the coast, in Palmeira or Santa Maria, where buzio stew and grilled fish are the island staples.

Scala dei Turchi
Italy
White marl cliffs sculpted into natural staircase steps, glowing orange at sunset above the Mediterranean.

Lampedusa
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Closer to Africa than Sicily, a wind-scoured island hiding a Caribbean-white beach.

Smögen
Sweden
A wooden boardwalk stretched over granite, where prawn peeling becomes a competitive spectator sport.

Piula Cave Pool
Samoa
Under the chapel, a lava tube pours cold spring water into a pool full of fish.

São Filipe
Cape Verde
A hundred pastel sobrados crowd the clifftop above a beach of jet-black volcanic sand.

Assomada
Cape Verde
Papaya, maize and market din fill the highland town that feeds all Santiago.

Vale do Paúl
Cape Verde
Sugarcane and coffee terraces pour off a crater rim into a valley threaded with running water.

Cidade Velha
Cape Verde
The tropics' first colonial city keeps its slave pillory standing in the square.