Once the homes of early humans, caves have always tickled the imagination. Their darkness, echoing caverns, hidden rivers, screeching bats and bizarre rock formations have become the setting of countless legends, stories and discoveries about times past. Bulgaria is no exception. This country's caves might not be the biggest or the most spectacular in the world, but many are very impressive and well worth a visit.

Before going underground, here are some hard facts. It is difficult to say exactly how many caves there are in Bulgaria – 5,000, 6,000 or even 10,000. Their diversity is impressive – from dark labyrinths stretching for kilometres underground to huge halls, picturesque stone arches and crevices of all shapes and sizes. The most expansive identified cave in Bulgaria, Kolkina Dupka, near Zimevitsa village close to Svoge, is 25.9 km long and 562 m deep, but it is not included in our list as it is not suitable for ordinary tourists.

Prohodna Cave

Where: Near Karlukovo
Wow factor: ****/*****

The Eyes of God: whoever came up with this name for the most impressive feature of Prohodna Cave, near Karlukovo, did a good job. The two openings in the ceiling of the cave really look like the gaze of a supranatural being. Some locals might protest that the actual, traditional name of the openings is the more prosaic Oknata, or The Chimneys, but bringing more visitors to this part of the economically depressed Bulgarian northwest is always a good thing for the local community.

Even without the Eyes of God name, Prohodna Cave is stunning. It is Bulgaria's longest cave passage, sneaking for 262 m. The ceiling is about 50 m high and its eastern and western entrances rise about 20 m and 42 m, respectively. The western entrance is the highest in Bulgaria.

Devetaki Cave

Where: Near Lovech
Wow factor: ****/*****

Devetaki Cave's majestic main cavern rises up to 60 m and covers an area of almost an acre, making it the largest of its kind in the eastern Balkans. Its size is not the only thing that awes visitors. Seven openings, large and small, pierce the rock dome of the main gallery, sending eerie shafts of light into the void. A spring murmurs through the cavity, its voice mingling with the squeaks of swallows and the shrieks of bats.

Neanderthals and early Homo sapiens inhabited the cave. Later, people kept their sheep there. This practice ceased in the 1950s, when the Bulgarian Army turned the cave into a secret fuel storage facility. The army moved out in the early 1990s and the cave has been open to visitors ever since. In the 2000s, it even became a film set, when some action scenes from The Expendables 2 were shot there.

Visiting Devetaki Cave is prohibited in June and July, which is the mating season of the local bat colony.

Devil's Throat

Where: In the Rhodope, near Devin
Wow factor: *****/*****

The Devil's Throat is not a cave you visit if you are after stalactites and stalagmites. You go there to experience the feeling of being deep beneath the earth's surface, where a 42-metre underground waterfall booms in a huge cavern and fills it with thrill and thunder. When it hits solid ground, the Trigradska River disappears into another hole, only to resurface miles away. Locals say that everything that has fallen into its waters – from animals and humans to entire timber logs – is doomed to disappear forever in its mysterious, infernal labyrinth. A humble plaque by the cave entrance, dedicated to two spelunkers who drowned there, shows that this belief is not without justification.

Visiting the Devil's Throat is not for the faint-hearted. The climax is at the end of the tour. Your only way out is via a narrow metal staircase that climbs beside the waterfall.

When there, you will inevitably believe the legend that when Orpheus descended into Hell in search of his lost love, Eurydice, he passed through the Devil's Throat.

Ledenika

Where: Near Vratsa
Wow factor: ***/*****

Located deep within the picturesque Vratsata Gorge park in one of the most impressive parts of the Stara Planina, Ledenika is a family-friendly experience. In just over 300 m of length, it offers ten halls covered with elaborate stalactites, stalagmites and other cave formations. Their beauty is undisputed and the acoustics of the so-called Concert Hall are used for regular music performances.

The cave's name, Ledenika, is derived from the Bulgarian word for ice and comes from the icy stalactites and stalagmites that form near the entrance in winter. In the past, locals used it to store milk from their sheep flocks.

Magura

Where: Near Belogradchik
Wow factor: ****/*****

Magura is packed with stalagmites, stalactites and stone columns, a small lake, plus a colony of eight bat species. Its outstanding feature, however, is its gallery of prehistoric drawings.

Magura is the only place in Bulgaria where cave art can be seen. These figures of people, animals, birds and geometrical shapes remain puzzling. Some scenes have been interpreted as hunts, others as religious rituals and possibly as a form of early calendar. How early is difficult to say. The Internet attributes some of the drawings to Neolithic and even Palaeolithic people but, according to historians, they date from much later, the 1st millennium BC.

Unfortunately, after some of the ancient images were vandalised, the rock art section of the cave was permanently closed to visitors.

Saeva Dupka

Where: Near Yablanitsa
Wow factor: ***/*****

Scores of stalactites and stalagmites crammed into a cave just over 200 m long: until recently, it was easy to go on an unplanned visit to this natural wonder. Before the construction of part of the Hemus motorway, traffic passed through the nearby village of Brestnitsa. In the village centre, brown tourist signs diverted curious passers-by on a short trip to the underworld of Saeva Dupka.

Today, the motorway bypasses Brestnitsa without a single sign for Saeva Dupka, so you will have to plan your visit in advance. Wandering among the cave's impressive formations is well worth it. There is a stalactone measuring 60 m in circumference, and the rocks inside are famed for their varied colours: white, green and brown. Behold the broken massive stalactites. They were shattered by an earthquake in 1893.

Like other popular caves in Bulgaria, this one also has a concert hall with good acoustics.

Stalbitsata

Where: Near Lovech
Wow factor: ***/*****

When you find the entrance to Stalbitsata, or Little Ladder, you might feel a pang of disappointment. Gaping in an overgrown field, it hardly looks promising, just another hole in the ground.

Once you descend the damp staircase that has given the cave its name, however, you will find yourself in a surreal setting: a moist, dark underground cavern lit solely by the light filtering through the narrow entrance.

Yagodinska Cave

Where: In the Rhodope, near Devin
Wow factor: ****/*****

Located in the gorge of the Buinovska River, Yagodinska Cave is advertised as Bulgarias most beautiful cave. It is 10 km long and spreads over three levels, but visitors are taken on a guided tour that covers only 1,100 metres on the lowest level. The path leads past stalagmites large and small, rock curtains and cave pearls. Here and there, the rock is covered in spots that spelunkers have dubbed leopard skin.

The most spectacular formations have their own, rather imaginative, names such as Snow White and the Seven Dwarfs, Virgin Mary and Baby Jesus, Father Christmas and so on. The cave is also a place for some eccentric traditions, including celebrating New Year's inside, with spelunkers leaving the festive tree in the cave for the whole year, and even getting wed.

God's Bridge

Where: Near Vratsa
Wow factor: ***/*****

In a region that appears stuck in its bad fortunes – depopulation, unemployment and lack of business opportunities, the presence of a place called God's Bridge appears illogical. The northwesterners often call themselves "god-forgotten." 

And yet, here it is – a 20-metre-long stone arch, a stunning sight when you watch it from the cavern below. God's Bridge was formed in the soft karst rocks near the villages of Lilyache and Zhabokrek by a small river, Lilyashka Bara. Of course, it has a legend attached to it: somewhere inside in the cave adjacent to the stone arch the gold loom of Roman Empress Helena lies hidden.

Bacho Kiro

Where: Near Dryanovo
Wow factor: ***/*****

The history of early Homo sapiens and other human species is constantly being rewritten. One of the central questions that still awaits a definitive answer is how and when our ancestors replaced the Neanderthals, who used to dominate Europe. 

A couple of years ago Bulgaria provided a piece of the puzzle, when an amazing discovery was made in a cave in the Stara Planina.

Human remains discovered in Bacho Kiro Cave showed the first evidence of Homo sapiens in Europe at a time when the Neanderthals were still thriving on the continent. The find indicates that the two species coexisted as early as 45,000 years ago.

The cave itself is also of some beauty and the nearby Dryanovski Monastery is a popular tourist site.