On its northwestern slope the small village of Altburg is situated, nearby the municipal boundary to Zürich-Affoltern and the Katzensee protected area.

The still visible massive walls of up to 4 metres (13 ft) width correspond to the essential features of the state after the third building phase.

The elevated entrance was on the west side of the tower and was originally accessible by a ladder and a simple wooden platform.

The outer casing of the 11th-century structure was filled with boll stones and mounted in horizontal mortar joints strokes.

Only at the end of the 12th century a circular wall was built which rested on a 2 metres (7 ft) wide foundation.

The oldest water pit was abandoned when the kennel was built, and replaced by the cistern in the southwest corner of the facility.

After flown through a layer of gravel, the filtered water was collected in the central bay and could be scooped with a boiler.

[2] The so-called Hunfried document of 1044 AD mentions among others a witness named Lütold von Affoltern who is suspected as the builder of the castle.

A visible sign of the upturn of the House of Regensberg was the decisive transformation of the castle as high medieval aristocratic residence with circular walls made of stone instead of palisades, and the elaborate shell of the keep.

After she married Johann Schwend, a citizen of Zürich,[2] the couple sold the castle to the merchant Rudolf Mötteli on 4 February 1458.

In his report Mötteli wrote to have installed six heatable rooms that he had provided with belt floors and wood paneling, glass windows, stove tiles, a new oven and a deeper cellar.

Other assets and rights were in the Limmat and Reppisch valleys, in Zürcher Oberland, in the Pfannenstiel area, also sporadically in the present Thurgau and north of the Rhein river and on Bodensee lake shore.

Two monastic foundations date back to the House of Regensberg: Around 1130 Lütold II and his wife Judenta and his son Lütold III founded the Fahr Abbey, and with the foundation of Rüti Abbey in 1206 the family probably secured lands of the first extinction of the Alt-Rapperswil family around 1192.

The Regensberger feud against the Habsburgs and the neighbouring city of Zürich in 1267/68 lead to the decline of the family that became extinct between 1302 and 1331.