Nynäs havsbad, building in Nynäshamn Municipality, Stockholm County, Sweden

Nynäs Havsbad is a seaside resort with a hotel, spa, and conference center located by the sea in Nynäshamn Municipality. The complex includes several buildings: Strandhotellet with traditional design, the yellow Badhotellet with modern rooms directly on the water, and Havspaviljong, a bathhouse on stilts in the sea with heated pools and saunas.

The main Badhotellet opened in 1906 together with Parkhotellet, followed by Strandhotellet in 1907 and a Casino in 1913. During the First World War guests stayed away and the complex fell into disrepair. In 1918 the Kungliga Pensionsstyrelsen acquired it for use as a hospital; the Badhotellet was demolished in the 1930s when the hospital was expanded with a large new building. The state sold the properties in 1999 and Nynäs Havsbad reopened in 2003 after renovation.

The name Nynäs Havsbad preserves the older spelling "Hafsbad", used when the railway station opposite Trehörningen was renamed in 1907. The station closed in summer 2008 and moved to Gröndalsviken. The resort hosted the base for the sailing events of the 1912 Stockholm Olympics, with races starting from Gårdsfjärden toward Viksten and Gunnarstenarna.

The resort offers rooms with direct access to the beach and nature, plus dining options featuring fresh local ingredients. The spa accommodates guests over 15 years old, though children can use some facilities during school holidays.

Havspaviljong is a bathhouse built on stilts in the water, where guests can view the sea from heated pools and in winter access an ice hole for swimming. This floating structure merges the spa experience directly with the surroundings, creating a rare blend of relaxation and nature.