Twr Bach (little tower) and Twr Mawr (big tower) are the two towers / lighthouses on the south-east and south-west tips of Ynys Llanddwyn.
Twr Bach has been there a little longer than Twr Mawr, though there seems to be no precise record of when either tower was built.
It’s also quite hard to find the truth about why the towers were built, but it seems Twr Bach was originally built as a landmark and day beacon (an unlit lighthouse). However, it was built in the wrong place – it couldn’t easily be seen by ships approaching from the west. Therefore, Twr Mawr was built to replace it.
Twr Mawr is on a higher, more westerly promontory and definitely more visible from most directions. As its name suggests it is bigger than Twr Bach, standing nearly 11m tall. The first navigational beacon was put in Twr Mawr in 1845 and it became a working lighthouse on 1st January 1846.
For nearly 130 years Twr Mawr continued as a lighthouse, while Twr Bach lay dormant at its side. But in 1975 when Twr Mawr ceased operation, Twr Bach became the site for the installation of a new, modern navigation beacon. So now, Twr Bach is the working tower, while Twr Mawr is a striking and iconic landmark for Ynys Llanddwyn.
The main footpaths on Ynys Llanddwyn both lead you to Twr Mawr. It’s about a mile and a half walk from the main car park at the end of the forest toll road. Be careful of the tides: when the tide is high, Llanddwyn is cut off for a while.
There is interesting information about the history of the towers at Coflein (The Royal Commission on the Ancient and Historical Monuments of Wales) and at tpwilliams.co.uk (a miscellany of local historical information).