The shaft of light
Sun falling through the collapsed opening straight onto the lake.
Matt Sims — CC BY 2.0 · Jean Housen — CC BY-SA 3.0 · Jean Housen — CC BY-SA 3.0 · Jean Housen — CC BY-SA 3.0
**An underground lake whose roof collapsed, so light now falls vertically onto the water** — near Sami, and the best-known sight on Kefalonia. The cave was originally sealed, but **part of its roof fell in** at some point, leaving a **large circular opening** above. When the sun is near vertical, **light drops through that opening straight onto the lake** — and the water turns an **electric, luminous blue**, with the boat appearing to hang in mid-air because the water is so clear. The visit is by **small rowing boat** worked by a local oarsman: he circles the open chamber and then rows into a **second, dark chamber** of stalactites and stalagmites. ⚠ The water is **brackish**: sea water that has seeped across the island from the other side, mixed with fresh groundwater. ⚠ And timing here is **absolutely decisive**.
Sun falling through the collapsed opening straight onto the lake.
Clarity that makes the boat appear suspended above the bottom.
A second room of formations the boat enters after the open one.
Karavomylos, 28080 Sami, Kefalonia, Greece
**Between 11 am and 1 pm — one of the few sites where midday is the right time.** ✅ **Why**: the whole effect depends on **sunlight dropping through the collapsed opening in the roof** onto the water's surface. That only happens when the **sun is high and near vertical** — that is, in the middle of the day. ✅ **What happens then**: the light strikes the water and reflects back up off the pale bottom, **lighting the lake from within**; the blue turns electric and the boat seems to float in space. ⚠ **Outside that window**: the light comes in at an angle and does not reach the water directly — so you see **a handsome cave with an ordinary dark blue lake**, pleasant enough but **not what you saw in the photographs**. ⚠ **The cost**: **everyone knows this**, so that same window is peak time — queues and waiting in August. ✅ **The best compromise**: **a clear sunny day around 11** — slightly ahead of the crush, with light enough.
**From the sea — having crossed the entire island underground, in one of the strangest hydrological phenomena in Greece.** ✅ **The phenomenon**: on the other side of Kefalonia, near **Argostoli**, are the **katavothres** — «swallow holes»: points on the shore where **sea water flows into the ground and disappears**. It puzzled people for centuries; in the 19th century it was even used **to drive watermills** with the force of the inflow. ✅ **Where it goes**: a **dye-tracing experiment** in the 1960s proved the water crosses **beneath the whole island** — through a network of fissures in the limestone — and emerges roughly **two weeks later** on the eastern side, at **Melissani** and **Karavomylos** near Sami. ✅ **On the way it mixes with fresh groundwater** coming down from the mountains — so the lake's water is **brackish** rather than fully salt. ⚠ **Why it flows at all**: pressure and level differences between the two sides drive it, and the limestone is porous enough to let it through.