Soos, Protected natural area in Křižovatka, Czech Republic

Soos is a protected nature reserve near Františkovy Lázně featuring mineral springs, peat bogs, and salt marshes across its landscape. Wooden walkways guide visitors through the different natural zones and geological formations found throughout the site.

Peat was dug here in the 18th and 19th centuries, and in 1870 pharmacists Adolf Czernicky and Albert Günther built a saltworks producing moor extracts, bought by Heinrich Mattoni's firm in 1872. Diatomite was mined until the 1950s. The site was declared a state nature reserve on 7 November 1964 and a national nature reserve on 1 February 2016, enlarged to about 262 hectares.

The name Soos comes from the Egerland German dialect word for moor or swamp; older spellings shifted from Sas(s) to Soos(s). The nearby Nový Drahov station is the start of the Kateřina mine railway museum line, which runs through Soos on selected weekends.

Wooden walkways provide safe passage through the sensitive landscape and should be followed at all times. Straying from marked routes is prohibited to protect the natural environment.

The mofettes lie where the Eger Graben meets the Cheb-Domažlice Graben, and the gas rises through funnel-shaped mud craters. Some craters line up in rows, which suggests they follow the course of small faults.