Ty-to-Maen was built in 1885-9 by E. Bruce Vaughan of Cardiff, who was also the diocesan architect. Sir William Edgar Nicholls, manager of Spillers, was the subsequent owner who presented the mansion and estate to the Cardiff Royal Infirmary for use as a convalescent home. The mansion is in Tudor/Gothic Revival style, built mostly of snecked rock-faced stone with Bathstone dressings; it has a mostly small slate roof with gable finials and terracotta ridge tiles. It is two storeys and attics, with a main frontage of 5 bays. There are mullion and transom windows and a 3 storey tower with embattled parapet, corbel table and gargoyles, and with a chequered band of ashlar and brick.

Photos of the convalescent home in use (1964) show a deep verandah stretching across right bay of frontage. Main interior rooms including reception hall and staircase were decorated by Campbell Smith of London, who also provided the stained glass, with stone carvings by William Clarke of Llandaff. In spite of institutional use, much of the rich interior fitting survives. Many rooms have decorative plasterwork, large ornate fireplaces, dark stained heavily moulded woodwork and lentiful stained glass mostly depicting naturalistic flowers and birds.

Now in use as a school known as St John's College.

RCAHMW, 2010.