Nendrum Monastery may have been founded in the 5th century, but this is uncertain. The monastery came to an end at some time between 974 and 1178, but its church served a parish until the site was abandoned in the 15th century. Some remains of the monastery can still be seen.
Dendrochronology has dated a tide mill on the island to the year 619, making this the oldest excavated tide mill anywhere in the world. The monastic site included orchards, gardens, pastures, arable fields, and a guest-house.
The principal monastic remains which can now be seen are three concentric cashels (enclosures) of dry stone walling, but these were substantially rebuilt by Lawlor in the 1920s. The central cashel has the round tower remains, a ruined church with a sun-dial, and a graveyard. The second cashel contains what is called a 'monastic school' or workshop and other burials.
The canonical sundial now seen at one corner of the ruined church was reconstructed from fragments found during the excavation of the site in 1924 and has been dated to about the year 900. One of only a few early medieval sun-dials known to exist, it takes the form of a vertical stone pillar, 190 cm high, 40 cm wide and 15 cm thick, with the dial and gnomon on one face at the top. However, because of the nature of the reconstruction, the original height of the pillar is conjectural.
Kakesbeck is one of the largest medieval fortifications in Münsterland and the oldest castle in Lüdinghausen. The imposingly grown complex originated in 1120 as a motte, a small hilltop tower castle. After numerous changes of ownership, the castle was extended onto two islands, but it was not until the 14th century that it underwent significant alterations and extensions under the von Oer family. The estate experienced its heyday in the middle of the 18th century, when it covered an area of almost one square kilometre and consisted of five further outer castles in addition to the core castle, which were secured by ramparts and moats.
The well-maintained condition of the castle today is thanks to the late Wilfried Grewing, the former lord of the castle. The foundation named after him has been particularly committed to preserving the property since 2020.