Saint Nicholas monastery and church, Medieval Dominican monastery ruins in Buda Castle Quarter, Hungary.

Saint Nicholas monastery is a medieval ruin in Buda Castle Quarter whose remaining walls and tower are now integrated into the Hilton Budapest hotel building. The visible stonework displays the Gothic architectural style of the original 13th-century construction.

The monastery and its church were consecrated in 1254, on the site of an earlier church or chapel dedicated to the Virgin Mary that served the early Hungarian settlement on the hill. A Dominican provincial chapter met there that year, and by 1305 the order's provincial college was installed. The Miklós Tower was built in the early 15th century, and a well in the cloister courtyard dates from the reign of King Matthias. The buildings were damaged in the siege of Buda in 1530 and the friars left; the remains were demolished before the recapture of Buda and the foundations and cellars filled in.

The monastery was consecrated in 1254, and a Dominican general chapter met there that same year. By 1305 the order's provincial college was installed in the complex. The site is reached as the Dominikánus udvar (Dominican courtyard) built into the Hilton hotel, where the excavated foundations and the Miklós Tower stand together.

The ruins stand on Hess András tér, reached through the Dominikanus courtyard built into the Hilton Budapest; the Miklós Tower and excavated foundations are visible there. The site is a short walk from the Fisherman's Bastion and Matthias Church. Parts of the remains lie below the hotel level, so look for the courtyard entrance rather than the main lobby.

The Mátyás monument copy on the tower's lower western side reproduces a stone carving kept in Bautzen, Germany; Kálmán Lux placed it there during his early-20th-century restoration of the Miklós Tower. The tower itself was built in the early 15th century, separate from the 13th-century monastery walls.