Soos Nature Reserve

Soos is a peat bog and former lake basin in western Bohemia sitting over a zone of continuing volcanic activity - the last eruptions in the region were only a few hundred thousand years ago and the ground is still degassing. Carbon dioxide rises through the water in mofettes, vents that bubble continuously and are called mud volcanoes locally, some of them building small cones of grey mud. Where the lake dried, mineral salts left a white crust over the diatomite bed, and the walk crosses it on a boardwalk about a kilometre and a half long through a landscape that is genuinely unlike anything else in the Czech lands. The gas concentration in hollows can be lethal to small animals, which is why the boardwalk exists and why leaving it is prohibited. There is a museum on the site and an enclosure with some animals, which sits oddly beside the geology.

What you actually see

• Bubbling mofettes - carbon dioxide vents rising through pools, building mud cones.
• A white salt crust - mineral deposits over the dried diatomite lakebed.
• A boardwalk of 1.5 km - the only permitted route across the ground.
• Continuing volcanism - the youngest volcanic zone in the country beneath it.

When to go

April to October. Half a day.

Honest expectations

Leaving the boardwalk is prohibited and dangerous - carbon dioxide pools in hollows. It smells of sulphur. Open seasonally with limited winter access. The site is small; two hours covers it.

Nearby

Frantiskovy Lazne spa is six kilometres away; Cheb is west.