During the improvement and archaeological survey works carried out near the Double Fortress Gate in 2015, remains of a bath-house attributed to late Middle Ages were revealed. It is located quite below the ground level therefore it is known as "the underground bath-house". According to researchers, customs bath-houses strictly following the sanitary and hygienic rules operated in Baku at that times. The bath-houses were built close to the main entrance. Highly likely, this bath-house served the Baku customs office. After Russian occupation of Baku in 1806, its operation was stopped, the dome was demolished, the rooms were filled with household waste and covered with earth. Thus, the military police was located there. In 2015, due to archaeological excavations, the main part of the complex was cleaned up of the earth, its architectural shape was identified. Cracks appeared on some remains of some walls and masonry at and it was exposed to a danger of destruction. Restoration and preservation works on the monument are underway. An archaeological museum exposition shall be accommodated therein.