Just to the east of Loch Olavat there is a minor road heading north, take it and then take the first road heading east. This, unsurprisingly, leads to a small harbour. Walk to the north side for a clear view of Dun Thomaidh.
What may or may not have been a broch but definitely a dun is in the Caolas Bhalaigh waters. It is connected to the island of Vallay by a large causeway. The small harbour is in the east presumably as it would be more sheltered.
It had been my intention to get to Vallay Island but there is hardly any information on safe crossing times. We couldn't find a signpost for the track across for this also. So a proper visit to Dun Thomaidh will happen in the future.