Baba Vida castle (Баба Вида крепост), sits in the unexciting town of Vidin, watching over a broad stretch of the Danube. When we arrived, on a still-hot evening as the sun was going down, there was a volleyball game happening on part of the outer wall. A few straggling sunbathers lay out on the grass (including a suspicious, naked man) and an elderly couple toweled off after their swim.
The fortress was serene and jumbled, a confusing cluster of towers, brickwork and walls. It's a mix of styles - Bulgarian, Austrian, Ottoman - and periods, with 19th century touches and old Roman foundations, still visible, underneath. We slept in town and came back in the morning to take a closer look.
Bulgaria once had many castles, but most are ruined - other than the sham castle in Veliko Tarnovo, this is pretty much the best the country has to offer. It's in great shape, with a grassy moat and pretty towers, a lot of history and a nice compactness.
Luckily, the main stronghold has remained, though it's in a much different condition than it used to be. The Ottomans, who ruled the region from the 14th to the 19th centuries, made the most changes, along with Austrian allies who occasionally were charged with the castle's defense.
As cannons became more common, castles began being built specifically for them. Older buildings, like Baba Vida, were often retrofitted - but any new structures had a decidedly different look to them than the antiquated, high-walled tower-cluster that had dominated earlier periods. High walls were great for archers, but terrible for big guns (I've covered a lot of this in more detail here and a little bit here). By the 1600's and 1700's, most medieval castles had been abandoned or completely overhauled. By the 1800's, they were almost completely obsolete - there was only so much one could modify an old fortress, most rulers preferred to build something new.
Baba Vida is different - it was used right up until 1865.