In 1965, Dimitar Kovachev, a biology teacher from the town of Asenovgrad, was on a field trip to Ezerovo village. A previous find of a mammoth tooth from a sandy area near the village had ignited Kovachev's imagination – palaeontology was a passion of his and the region was known for its fossils from the Miocene and the Pliocene, geological periods that lasted roughly between 10 and 2.6 million years ago. So he was there, with a group of students, on a hunt for more fossils.

The grand staircase of Sofia University’s central building. It will not take you to the Museum of Palaeontology and Historical Geology and its deinotherium (next spread), but go and see it nevertheless – it is yet another hidden gem

The team did find something near Ezerovo. None of participants was prepared for the monumentality of their discovery – an almost intact skeleton of a deinotherium. Deinotherium was one of the largest land mammals to roam the earth. It was similar to another, better known, prehistoric giant, the mammoth, and was almost as big. The animal discovered by Kovachev weighed about 14 tonnes and was over 7 m long and 4.5 m high. Unlike mammoths, deinotheriums had shorter tusks that pointed downwards and backwards.

The Ezerovo find was a new, separate species that dwarfed other members of the Deinotherium genus. Today, its scientific name is Deinotherium thraceiensis Nikolov, after Thrace, the region where it was discovered, and the palaeontologist who restored the skeleton in the course of seven years.

The restored deinotherium became the star exhibit of Sofia University's Museum of Paleontology and Historical Geology. It caused quite a stir in Bulgaria at the time. A documentary was made about the restoration process and a scaled replica of the skeleton toured international scientific events, gathering praise for its quality craftsmanship.

Quaint and often unkempt, Sofia's University central building feels labyrinthine and lost in time

Then, gradually, almost everyone forgot about the giant's skeleton that stood under the roof of Sofia University's central building, surrounded by cabinets and shelves of other, less spectacular fossils.

The deinotherium is still there: at the end of the grand marble stairs that lead up to the fifth floor of the north wing of Sofia University's main building. The place is almost always empty, in contrast with the lively corridors beneath. Buzz the button to enter the museum, on workdays between 10 and noon and 1 and 4 pm.

Dimitar Kovachev, the founder of deinotherium, was luckier than its find. In the years after his spectacular discovery, he started regular paleontological digs and found some of Bulgaria's richest fossil deposits. His other discoveries include a new species of prehistoric bear, an almost entire skeleton of sabre-toothed cat and the sole remains of a now distinct mammal called Kalimantsia bulgarica – an ant eater-like animal that was about 3 m high. Initially, Kovachev displayed his finds in the Asenovgrad school where he taught. Eventually, the Bulgarian Academy of Sciences helped him open a proper paleontological museum in Asenovgrad. It now bears his name and has a scaled replica of his most spectacular find – the deinotherium.