The caves exist.
The caves were neither secret nor recently discovered.
In early March 2017, multiple outlets covered the purported discovery of Knights Templar caves they suggested were found down a "rabbit hole" in the western England county of Shropshire:
Caverns used by the shadowy warrior monks 700 years ago are just a few feet inside a rabbit hole ... Once used as a ceremonial spot for the followers of a secretive religious sect, these are the underground caves offering safe haven after leaders of the free world brutally dismantled the group's power base.
The caves in Shropshire were once a place of pilgrimage and worship for followers of the Knights Templar, a feared fighting force during the Crusades who built an international power base on their reputation and spoils.
The untouched caverns date back to a time when the Knights were prominent before King Philip IV of France, fearful of their power and deeply in their debt, attempted to dismantle the renowned group.
The BBC reported that the "mystery caves" were discovered down a "rabbit hole," hinting that the caves were a brand-new and unexpected discovery:
An apparently ordinary rabbit's hole in a farmer's field leads to an underground sanctuary said to have been used by devotees of a medieval religious order - but is everything what it seems?
According to local legend, the Caynton Caves, near Shifnal, in Shropshire, were used by followers of the Knights Templar in the 17th Century.
Located less than a metre underground, they appear to be untouched structurally.
Buried at the very end of the BBC's article was an indication that the caves were not actually a new discovery, saying that they were reportedly "sealed up in 2012 in a bid to keep away vandals". Extensive documentation of the caves appear on the internet, with one series of images taken by a visitor in 2009. A network of Shropshire caves (including the "new" discovery) were examined in the 2002 book Subterranean Shropshire.
Some outlets covered issues with trespassing that led to the closure of the caves in 2012, then again reported them as a new find in 2017. The 2012 stories noted that the caves were likely created as a Victorian-era "folly," and didn't tack on the connection to the Knights Templar (a Christian military order active between 1129 and 1312) for another few years. The Birmingham Mail took an extra step of replacing its 2012 coverage with the more mysterious 2017 version (archives remained), but other outlets did not.
That general description was repeated on an undated ShropshireHistory.com page, which says that the caves were a Victorian-era creation:
This is an underground folly cut out of sandstone to create a temple. It is not known when or why it as built but it was probably created as a folly in the mid-19th Century when this sort of thing was fashionable. The landowners used to allow the public to explore the temple but damage and litter caused by visitors finally made them seal up the entrance.
Although the caves were reported as a new find in 2017, they were not new, not secret, and not widely thought to be more than a couple of centuries old.