It is difficult to find the place in the city and near it, where would not be mines for extraction of limestone - the catacombs. Catacombs are mostly everywhere, so even in the areas where, according to available data, officially extraction was not conducted, we can not deny the existence of old catacombs.
So why were large limestone mines placed in Odessa? In treeless areas near the Black Sea limestone was the most accessible and cheapest building material. Another local material, brick, costs considerably more expensive, so the limestone was the main material which was used for the construction of the city until the 50-ies of the XX century. Limestone is lightweight, cheap and warm. One piece of limestone is equal to twenty bricks that make faster and easier the process of building. Built with limestone houses had only 3-5 floors. That’s why it has always been forbidden to build skyscrapers in Odessa. Odessa catacombs consist of several types of undergrounds, sometimes closely linked with each other. These are mainly underground mines, which were getting building stone - saw limestone. Mines are approximately 95-97% of the total length of the maze of Odessa catacombs. There are also known for exploration different underground galleries, shafts, military bunkers, tunnels, drains, cellars for various purposes, rain collector tunnels, water wells, cisterns, natural caves and others. All this, uniting with each other, form Odessa catacombs. But, unfortunately, under Odessa absent the "True catacombs” - artificial underground structures cult destination. As I said the total length of the Odessa catacombs constitute 2500 kilometers. In fact, it is the biggest handmade underground system all over the world.

I think that you understand that in order to explore such a huge maze, you need to spend years. Some people devoted their lives for this.
The first known information about the exploring Odessa catacombs belong to 1846, when paleontologist A. Nordman in "Tarasovsky mines” conducted paleontological excavations in several caves exposed by mines. Later in 1869, these caves were explored and described by the geologist P. Barbot-de-Marne. Survived several descriptions of mines made during 1830-1870s. The first expedition for exploring the catacombs, or "mines" as they were called was organized by the city administration in 1875. The results of this expedition were photos of catacombs and descriptions to them. Unfortunately, these documents have been lost and have not been found yet.
The next expedition to explore the catacombs was established in Soviet times, in 1929. The expedition was formed at the direction of the All-Ukrainian Central Executive Committee of the Odessa City Council. Its membership included geologists, historians, police. The expedition was headed by T. G. Gritsay. The expedition worked from September 1929 to March 1930. During this time were investigated 49 mines, dropped plans for about 40 km of catacombs, photographed 45 objects. In general expedition answered to the question of what constitute Odessa catacombs. Later T. G. Gritsay, until the end of life (1980) was interested in catacombs. Unfortunately, the results of his activities were not preserved and they can only be judged on several documents and indirect data. By the way, graphics and descriptive materials of the expedition in 1929 also were not survived. There is only general information of the work of this legendary expedition.
After the expedition of T. G. Gritsay Odessa catacombs for many years have not been studied. There are however some facts that in 1932 Gritsay headed unknown Kiev expedition, engaged in the catacombs, but it could be false. After Gritsay catacombs, of course, were attended, but this was done sporadically in small areas and with out any ideas of exploration. Surveyed only those sites on which it was scheduled to hold fasteners or mining (tunnel) works. In the first half of 1960s was organized Odessa landslide management, whose task was to combat the harmful effects of the catacombs on buildings and structures in the city. In this period Arkady Ivanov did a lot for a proper understanding of "the problems of the catacombs."

Almost in the same period with the landslide control, a little later, in August 1965 was organized by the Komsomol youth expedition "Search" («Поиск»). Their main task was to explore places of military glory in the catacombs. The organizer, head and soul of the expedition was Valery Yakovlevich Yudin. The original purpose of the "Search" was to study the events of war and revolution, associated with the catacombs, searching for sites of basing groups of soldiers and collecting of relics of those times. But very soon, by the spring of 1966, the sphere of interests of "Search" expanded to include a work for exploration of the catacombs, their mapping, collecting information on the technical workings and location of the entrances to the catacombs. Nowadays, underground exploration in Odessa catacombs is not on the high level. Unfortunately there are less than 50 explorers that like catacombs and explore them.