Vjetrenica Cave is the largest known speleological system in the country, characterized by complex karst morphology including subterranean lakes, speleothems such as stalactites and stalagmites, and active hydrological processes. To date, 7,014 meters of its passages have been surveyed using standard speleological mapping techniques. The cave extends from the margin of Popovo Karst Field toward the south, following major structural and lithological discontinuities within the limestone massif. Geological and geomorphological analyses suggest that the system may continue toward the Adriatic Sea in present-day Croatia, potentially spanning 15-20 kilometres beyond the currently accessible entrance. This hypothesis is supported by regional groundwater flow patterns and the orientation of the cave’s main channels.

            Vjetrenica is both a significant natural site and an important archaeological locality. Among the many archaeological discoveries are the remains of cave bears and leopards, as well as cave drawings estimated to be around 10,000 years old. One of the cave’s most striking features is the strong "wind" felt at the entrance. This phenomenon is actually an air current created by the difference between the cave’s constant internal temperature and the variable temperature outside. During the summer, warm air enters through deep cracks on the surface above the cave, cools as it moves through the underground system, and then exits through the main entrance as a noticeable airflow.

            Stalagmites form when mineral-rich water drips from a cave ceiling and deposits tiny layers of calcium carbonate on the floor. Over thousands of years, these layers build upward to create towering formations. Their shape and size reflect the cave’s water flow and mineral content. The remains of eight fossilised animals have so far been discovered in Vjetrenica Cave, including the Cave Bear (Ursus spelaeus), the largest species found there. The most remarkable find is the only complete skeleton of the European Ice Age Leopard (Panthera pardus spelaea), which roamed Europe during the Late Pleistocene.

            Vjetrenica is the richest cave in the world in terms of subterranean biodiversity, home to at least two hundred different species, many of them endemic and first discovered in this cave. Among its most extraordinary inhabitants is the olm (Proteus anguinus), a pale, eel-like amphibian perfectly adapted to life in complete darkness. Lacking functional eyes, it relies on highly developed senses of smell, hearing, and electroreception to navigate and locate prey. Its skin has no pigment, giving it a pinkish or white coloration, which is why it is often called the "human fish". The olm feeds on tiny cave invertebrates such as crustaceans and insect larvae, detecting even the faintest vibrations in the water. Because food in caves is scarce, it has an extremely slow metabolism and can survive for years without eating.
            Olms breathe mainly through their external feathery gills but also absorb oxygen directly through their skin, which is highly efficient in cold, oxygen-rich underground water. Their lungs are not the primary respiratory organs and are considered rudimentary, but they function as a useful backup system when needed. The species is also famous for its extraordinary longevity, commonly living more than 60 years, with some individuals believed to reach 100 years. Reproduction is rare and slow: males deposit a spermatophore on the cave floor, which the female takes up to fertilize her eggs. She usually lays 10-20 eggs attached to underwater rocks, and the embryos develop very slowly in the cold cave environment. In unusual cases, olms may even give birth to live young. Retaining their larval gills for life, they remain fully aquatic and move carefully to conserve energy. With no natural predators in the depths of Vjetrenica, the olm thrives in silence and darkness, symbolizing the remarkable evolutionary adaptations of the Dinaric karst underground world.

            Trebinje is a historic town whose origins date back to antiquity, with traces of Illyrian, Roman, and medieval settlements found throughout the region. Its old town developed under Ottoman rule in the 18th century, leaving behind stone houses, narrow streets, and the beautiful Arslanagić Bridge as lasting architectural heritage. During the Austro-Hungarian period, Trebinje expanded with new administrative buildings, fortifications, and urban planning that shaped its modern appearance. The town’s strategic location near major trade routes made it an important cultural and commercial center for centuries. Today, Trebinje preserves this layered history in its monuments, architecture, and traditional way of life.

            This pretty little city, largely untouched by tourism, will steal your heart with its authentic charm and postcard-perfect streets. The Old Town of Trebinje was established in the 18th century by the Ottomans and soon developed into a trading and crafts center known as Kastel. The most important figure in the development of Trebinje’s Old Town was Osman Pasha. He envisioned the town as a fortified settlement and constructed the moat that encircled the walls and flowed into the Trebišnjica river.

            Osman Pasha’s legacy in Trebinje included the construction of the mosque, a maktab (elementary school), and a madrasa (high school), which were the city’s first educational institutions. Built by craftsmen from Dubrovnik, the Osman Pasha Mosque features Mediterranean architectural elements and is renowned for its spacious interior and its 16 meter high octagonal stone minaret, considered one of the most beautiful in Herzegovina.

            After the mosque was completed, Osman Pasha was accused in Istanbul of building a mosque more magnificent in his own name than for the emperor. For this, Sultan Ahmed III ordered the execution of Osman Pasha and his nine sons in 1729. Osman Pasha was executed in Istanbul after his plea for pardon was denied. This tragic event highlights the extreme measures taken by the Sultan to maintain absolute control and deter any perceived insubordination. The elimination of an entire family line - a form of collective punishment - was intended to prevent potential claimants to power or acts of vengeance.

            Arslanagić Bridge is Trebinje’s most famous Ottoman monument and a standout example of 16th-century Balkan architecture. Built in 1574 by Mehmed-Pasha Sokolović to honor his son, who was tragically killed in a battle with Venice, the bridge has long connected the town with surrounding regions. After the Turks were driven from Herceg Novi in 1687, many families relocated to Trebinje, including Arslan-aga. He was granted land east of the town and tasked with collecting the toll for crossing the bridge. Over time, the bridge became associated with him, and it has been known ever since as Arslanagić Bridge, a symbol of the town’s history and Ottoman heritage.

            Trebinje’s plane trees are one of the town’s most recognizable symbols, creating deep natural shade and giving the city its distinctive charm. The famous summer patio Platani is an oasis during hot days, where visitors can relax beneath trees that are more than 120 years old. The natural canopy of these 16 impressive plane trees makes this square a unique and beloved meeting place for all generations.

            Along the Trebišnjica River, traditional irrigation wheels, known as "vodenice", have been used for centuries to divert water for agriculture. These wooden or stone wheels lift water from the river into canals, supplying fields and orchards in the surrounding area. They are not only functional but also a charming symbol of the region’s historical agricultural practices.

            The Trebišnjica river is one of the longest sinking rivers in the world, flowing through southern Bosnia and Herzegovina. It has carved deep valleys and lush landscapes, shaping the region’s natural beauty and supporting local agriculture. The river is famous for its underground course in the Dinaric karst, disappearing and re-emerging through numerous caves and springs. Trebišnjica has played a crucial role in the history and economy of towns like Trebinje, providing water for mills, irrigation, and hydroelectric power.

            The remains of the famous medieval town of Mičevac are located on the right bank of the Trebišnjica river. According to legend, the town was built by Duke Mičeta, after whom it was named. Mičevac consisted of a fortress and a suburb: the fortress was situated on a small hill, dominating the surrounding area, while the suburb lay below it. According to Lukari, a Dubrovnik chronicler, Mičevac was first mentioned in 1042. The town held an extremely important strategic position, protecting the communication routes that connected Dubrovnik with the wider hinterland. Records from 1445 and 1451 mention the existence of customs in Mičevac, highlighting its economic and commercial significance.