Ardencaple Castle Light, Scotland
FREE DOWNLOAD: A DETAILED POSTER-MAP WITH THE TRAVEL TIPS TO THE ARDENCAPLE CASTLE LIGHT 
Apparently, this is the oldest building in Helensburgh.
This square tower is all that remains of Ardencaple Castle, the traditional home of Clan MacAulay from the 13th-18th century.The 12th hief died in 1767 and the Clan descended into dormancy.
Today the tower is used as a lighthouse- the navigational beacons and transit lights for the Royal Navy, hence the name - Ardencaple Castle Light. The location is marked  on a map-guide that's free to download