Regnaholm, Manor house in Finspång Municipality, Sweden.

Regnaholm is a manor house whose main building and two wings stand on a peninsula in Lake Regnaren in Finspång Municipality. The castle-like main building was erected in the 1760s in Hårleman style for chamberlain Axel Gyllenkrok. A fire on 7 May 2017 destroyed the attic and the second floor.

Regnaholm was acquired from the crown by riksrådet Clas Åkesson Tott the Elder and passed to his son-in-law Johan Månsson Ulfsparre; it stayed with the Ulfsparre family until 1745, when the Gyllenkrook family bought it. In the 1760s kammarherre Axel Gyllenkrok had the palace-like manor built in Hårleman style. The Gyllenkrooks owned it until 1873. After standing empty for 40 years, it was bought in 1966 by Bengt and Lillemor Sjöberg, who restored it with their son Lars Sjöberg to an 18th-century appearance. A fire on 7 May 2017 destroyed the attic and second floor.

The mansion displays French-influenced architectural elements from the 18th century, visible in its symmetrical form and elegant details. These design features continue to shape how the building looks and reflect the artistic taste of its builders.

The main building and its two wings stand on a peninsula in Lake Regnaren, in Regna parish, Finspång Municipality. The upper floor and attic were damaged in a fire on 7 May 2017, so check in advance which parts can be visited. The grounds hold the parent tree of the Gyllenkroks astrakan apple.

In the south facade's second-floor window, many claim to see the silhouette of Major Johan Göran Gyllenkrok, the "Gubben i rutan". Some dismiss it as a tall tale; others hold that a lightning strike made the glass record the colonel's image. The 7 May 2017 fire damaged the attic and second floor.