Royat's Valley of Water and Lava

Grotte du Chien

A lava cave where carbon dioxide pools at floor level, once shown to spa visitors with a candle and a dog.

You're standing at the mouth of a cave that built this valley's early fame, and its name comes from an experiment that sounds like a stage trick. The cave opens in basalt, and volcanic gas still seeps from cracks in its floor. That gas is carbon dioxide, heavier than air, so it settles in a low layer along the ground. A person walking in upright breathed clear air and felt nothing; a dog at ankle height took in the gas and collapsed.

Spa visitors were shown exactly that, carefully, alongside two gentler proofs. A candle held near the floor went out at once, and soap bubbles floated on the invisible gas as if on water. The same gas is what makes Royat's springs fizz. The cave ran as a paying attraction until 1986, had one more short spell of visits in the 1990s and early 2000s, and now opens only on rare heritage days, so today you read it from outside.

The dark doorway is still here, at the eastern end of the thermal park, the first stop in a gorge that leads you west.

Thermes romains de Royat

Roman baths uncovered in 1881 during work on the railway viaduct, with three pools in a line, hypocaust-heated rooms, and one pool with steps and hemicycle seating still visible.

Look for the low walls and the single pool that still holds its shape; you are on the edge of a Roman bathing complex far larger than what remains. The baths came to light in 1881, while workers were building the railway viaduct that crosses the valley beside you. What they uncovered covered about 2,800 square metres. Three large pools sat in a line on one axis, and four rooms were heated through the floor by a hypocaust, the Roman system of hot air moving beneath a raised floor.

The rooms were finished with coloured marbles, mosaics and statues of bronze or marble. Later building work destroyed most of the site, but one pool survives with its steps and hemicycle seating, and it is still visible in front of you now. The remains have been a listed historic monument since 1889. The real story here is continuity: the Romans came to this narrow valley for the same warm mineral water that later filled the Belle Époque baths a few steps away.