I visited Villefranche-de-Conflent in August 2017. The town is awfully picturesque (it is also on the register of the Most Beautiful Villages in France) and very tiny, literally two streets and a square.

The components of the WH site brought mixed impressions. The ramparts are very imposing when viewed from outside the city walls, but I found touring them slightly disappointing: for all the history and all the good preservation, you basically end up walking a couple of kilometers of pathways of different width, with very little to see except a few largely empty courtyards and chambers. If you are expecting elevated perspectives of the town, you will not find much to choose from.

Cova Bastera is a cave complex ending in a fortified chamber overlooking the town. It is the only component that offers free entry. The caves pale in comparison to the nearby Grotte des Grandes Canalettes (which has nothing to do with Vauban), so make sure you visit Cova Bastera first.

Fort Liberia high above town takes about 20 minutes of climbing up the stairs even from the most athletic. It is certainly worth an effort. Inside, there is a great example of a self-contained military post, with barracks, service areas, a church, and beautiful crenellations. If you descend by the underground passages (750+ steps, not for claustrophobic), you will come upon an open landing with unobstructed panoramic views over the town.

Time allowance for all components of the WH listing: ~3 hours. I ended up spending nearly 8 hours in the tiny town, but that included the aforementioned Grotte des Canalettes and a very long lunch. The latter scuppered my plans to also visit the nearby Mont-Louis, but I expect that a more disciplined traveler should be able to accomplish both in one day if so desired.