When visiting Twmbarlwm Hillfort (known locally as 'the pimple') it is worth having a look at the cairns which can be seen to the east of the Hillfort.
Access is easy enough – just follow the track north (which runs to the east of the Hillfort) and the cairns are on the right hand side of the track, behind a fence. The cairns are quite prominent, covered in grass. I visited the cairns about 2 years ago so can't remember exactly how big they were but I do remember they were a fair size and easy enough to spot. I wouldn't say it was worth the effort to visit the cairns specifically but they are certainly worth a look when visiting the Hillfort. Parking is easy.