Tik-kuyu, Water well in Bakhchysarai Raion, Ukraine.

Tik-Kuyu is a siege well cut into the limestone of the Chufut-Kale plateau in Crimea. A vertical shaft 1.8 m wide at the mouth drops to a spacious floor with an altar and two small connected basins. From there a sloping gallery over 120 m long, angled at 22°, climbs to a second entrance near the Small Gates, ending in a vertical spiral staircase. The gallery vaults bear natural stalactites and walls are covered with Karaim cursive, Hebrew square script and Latin inscriptions.

Mentions of a siege well at Chufut-Kale appeared in Karaite histories, and M. Ya. Firkovich described a "tik-kayu" near the Small Gates in 1907, but its location was lost and many scholars treated the account as legend. A search excavation begun in August 1998 found the shaft mouth on its second day; work through 2001 cleared 25 m of limestone rubble and opened a gallery leading to a second entrance near the Small Gates, as Firkovich had written.

The name Tik-Kuyu is Turkic for "vertical well", and the sloping gallery was called Altyn-Merdven, "golden staircase", a measure of how precious water was inside the fortress. The walls of the underground passages carry inscriptions in Karaim cursive, square Hebrew script and Latin, left by the Karaims and others who used the site.

The shaft mouth lies on the slope outside the fortress walls, while the underground gallery is entered from the plateau at Burunchak; the lower exit opens near the Small (Southern) Gates. The gallery was fitted with railings and lighting by the Onyx-Tour speleotourism centre, so the route is walked on foot through a long inclined passage and a vertical spiral staircase.

During the 1998–2001 excavation of the shaft, diggers found a ceramic jug holding 4,287 coins, the largest coin hoard then known from Ukraine. It held 30 gold pieces, including Venetian ducats and an Egyptian sultan's dinar, plus silver Jochid dirhams and coins struck at Caffa, Crimea and Kyrk-Or.