The remains of the Castle can be visited
Alt-Süns Castle

The castle ruin Alt-Süns is situated on the western edge of the village of Paspels. Its origins date back to the 13th century.
History+
The visible wall remains of Alt-Süns Castle are dated to around 1200. It is believed that the Barons of Vaz founded the castle, in whose possession it was documented in 1285 as "castrum Sunnes". After the death of the last Vaz, Donat, in 1337, the complex passed to the Lords of Werdenberg-Sargans. In 1365, Ursula von Werdenberg and her son Johann temporarily pledged the castle to the House of Matsch, before it returned to the Werdenbergers at the end of the century. Its fate was sealed by the Schams Feud in 1542, an uprising of the valley people against the rule of the Werdenberg family, to which the castle fell victim. Reconstruction was omitted, as the approval of the Leagues would have been required for this.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://de.wikipedia.org/wiki/Datei:Alt_S%C3%BCns_Lage.jpg
This description draws on the facts documented in the linked Wikipedia article; Wikipedia content is licensed under CC BY-SA 4.0. Wording and editing: Mobile History.
Location: 46.7494, 9.4392