The number of visitors to the cave, which is its main tourist attraction, increased by 13% to almost 780,000 from 2016, the company said in a press release on Thursday.

The Postojna Cave, which has kept visitor records since 1819, welcomed the 38 millionth visitors in November.

The total number of visitors to all of its attractions - Predjama Castle, Proteus Vivarium, EXPO Cave Karst Pavilion - reached 1.2 million.

Italians accounted for the largest share of the visitors (16%), followed by Germans (8%), Slovenians (7.5%) and South Koreans (7%).

The cave remains the most globally recognizable Slovenian tourist attraction, having welcomed tourists from more than 150 countries last year.

Predjama Castle, a unique mediaeval castle built into a rock just outside Postojna, was visited by a record 240,000 tourists.

However, a milestone for the company in 2017 was the acquisition of Certa Holding, through which it become an owner of Cerkno Hotel with a ski slope and a spa.

This will enable it to expand its tourist portfolio to winter tourism.

Last year, the company invested 960,000 euro to improve the cave's infrastructure and another 1.75 million into other investments, CEO Marjan Bategalj told a news conference last month.

Investments for 2018 are planned at 2 million euro.

Batagelj also said the company expected similar results in 2018, when the number of visitors is to grow by 4-5%.

This year will be especially festive as the company is planning a series of events to celebrate 200 years since local Luka Čeč discovered the cave.

The discovery paved the way to the development of tourism in Postojna, at the time known as Adelsberg, and in Slovenian lands.

As early as 1819, the cave had a high-profile visit by Habsburg Prince Ferdinand I, who is credited with being the first visitor to the cave.