Frustuna kyrka

The church was built in the 12th century using natural stone, originally comprising a nave, a narrow chancel and a west tower. Substantial rebuilding took place in the 1300s and 1400s, enlarging the structure, adding windows and raising the tower, along with a new sacristy. Further changes followed: the spire was replaced by a saddle roof in the 1600s, windows were enlarged in the 1790s, and the roof was reclad in tile in 1801. A significant remodelling under architect Fredrik Lilljekvist in 1897 altered the tower's profile, added a round window to the east gable, and introduced a pulpit, pews, and wall and vault paintings in a Gothic-revival style. A restoration in 1939–1940 reversed many of these 1890s changes, and it is the late-medieval star vaults and the altar cabinet that give the interior its present character.

Among the church's furnishings is a sandstone font thought to date from the 1100s, which was reportedly found discarded in the churchyard before being returned to the church by the parish in 1868. The altar cabinet was made in Antwerp in 1510. The pulpit, created during the 1939–1940 restoration and carved with reliefs by Gunnar Torhamn, incorporates elements salvaged from an earlier 1708 pulpit that had been removed in the 1897 renovation.

Several carved gravestones are set into the church walls and floor, commemorating local landed families including the Kruse, Ehrencreutz, Rossfelt and Andersson families, with inscriptions recording names, heraldry and, in one case, a number of infant children and siblings buried beneath the same slab. The church also holds notable silver, including a gilded chalice and wine jug linked to the Kruus and Horn families, and a richly ornamented silver jug bearing portrait medals connected to Gustav II Adolf and Maria Eleonora.

The church's organ has a layered history: an initial instrument by Gustaf Andersson was installed in 1845, replaced in 1925 by an organ from E A Setterquist & Son, subsequently rebuilt several times through the 20th century, including work attributed to Olof Hammarberg in 1950. The current organ, built in 1980 by Walter Thür Orgelbyggen, retains a façade from the 1845 instrument.

Outside, near the churchyard's north gate, stands a runestone known as the Frustuna stone (Sö 10), carved from red granite and inscribed as a memorial raised by three brothers to their father. Until 1885 the stone reportedly formed part of the sacristy floor, and it was moved to its present position during the 1897 restoration. Other runestone fragments have also been found at the site, and the stone's original purpose - whether as a memorial or building material - remains uncertain. Nearby stand the former rectory (Frönäs), a parish hall, a churchyard stable and other associated buildings from the 19th and early 20th centuries.