The stone mushrooms. That describes them perfectly. They are maybe 3 metres high. The stems are relatively soft stone and the top bits a harder rock. A result of differential erosion and amusing.
After seeing these we returned to recharged our bike batteries and continued. To start with agricultural land in a valley, but it could not and did not last. Up and up again and at one point we had a long view to the North across central Bulgaria. Down then up including a marvellous bit of brand new road where the map said low grade road. Got to the site of an old Thracian stone circle. Actually this was a good mile up a footpath and we wouldn't have found it but for directions by a shepherdess. It was an emotive place.
To the vulture centre by the river Arda for overnight. Learned a bit about vultures and their importance . Saw a Griffin vulture on a high cliff with the help of the warden and his high magnification telescope.
Next day, down the Arda gorge until we had to climb out of it. Up, Northwards to cross another ridge. At the top, Thracian niches carved on a cliff; we looked for them to no avail.
Then on to Merek village with the by-now glorious descent on the way
Here is a well preserved Thracian "beehive" tomb, a underground passage to a well formed round chamber. The artifacts found there are in various museums but the place was well worth seeing.
Then to the edge of Svelengrad for overnight before across to Greece next day