Early this week I was staying in Thanjavur (Tanjore) for a few days. On Monday I went to see Thirumayam fort (திருமயம் மலைக்கோட்டை) which is on the way to Karaikudi from Tanjore. The fort was built in the 17th century by Vijaya Raghunatha Sethupathi, the Raja of Ramnad and it was in this fort that Oomathurai the brother of Panchalankurichi chieftain Kattabomman was captured by Britishers. The fort is well maintained under the care of the Archaeological Survey of India, it even has clean toilets with running water – a rarity in tourist places in India. On top of the hillock inside the fort, you will find a cannon barrel supposed to be used by the Britishers.

Venkatarangan with Thirumayam Fort walls

Climbing the rocky hillock is a bit difficult but not tough, takes about a few minutes to reach the top

Thirumayam fort walls

The modern-day gate to the top of the fort
As you enter the fort, to the side of the path to the cannon barrel you will see a cave which has an idol of Lord Siva (சிவலிங்கம்) which you can reach by climbing up a steel ladder.
Behind the back of the Thirumayam fort (detailed blog) entrance, you will find Sathyamurthi Perumal Temple [ஸ்ரீ சத்யமூர்த்திப் பெருமாள் திருக்கோயில், திருமயம்].
[Update: 16th February 2022]
Today en route to Rameswaram, I visited this fort again and took the pictures below.

Thirumayam fort walls with the moat below

Steps to climb to the top of the Thirumayam fort

ASI has been maintaining the Thirumayam fort well, you even have clean and functional washrooms!

A big boulder in Thirumayam fort

Another big boulder in Thirumayam fort

See the strong fort walls of Thirumayam fort

A cannon on top of the Thirumayam fort

The long cannon (பீரங்கி) on top of the Thirumayam fort

View of the town below from the top of the Thirumayam fort

An idol of Lord Siva (சிவலிங்கம்) in 2022 inside the Thirumayam fort