Reconstruction drawing by Falcon Hildred showing Gwastadannas as after the alterations of the late 16th century, including the insertion of a chimney and ceiling.
The old house of Gwastadannas is a modest single-story and attic stone house, part of a large farmstead situated on the Afon Glaslyn valley floor in Nantgwynant, Snowdonia. Although now much altered, a survey of 1953 found that the house had features showing that it had originally been a hall-house of some status and a plan was published in the Royal Commission's Caernarvonshire Inventory of 1956. Recent tree-ring dating for the Dating Old Welsh Houses Community Project has pinpointed the felling date of the timbers to 1508.