Swietojanska Street była niegdyś jedną z ważniejszych ulic staromiejskich. Mansionaria (under no 2) from the 2nd half of the 15th century was rebuilt in the spirit of the Renaissance by Italian architects Antonio Visconti and Bernard Morando (w 1688 year), and restored in 1918-1920 by arch. Juliusz Nagórski (discovered stucco decoration) and in years 1950-1953 by arch. Władysław Jastrzębski. The tenement house has a portal and gothic and renaissance window frames. The remaining tenement houses on this street were built in years 1947-1958, nadając fasadom formy z XVI-XVIII wieku i wmontowując zachowane portale. Townhouse “Under the Ship” (at the number 31) decorated with a late Renaissance portal and a bas-relief of a sailing ship – trade emblem (it is a reconstruction of a destroyed decoration from the 1st half of the eighteenth century). Tenement house at the number 11 has a decoration by Piotr Kann (stucco frieze with putts, coat of arms of Warsaw and sculpture “Warsaw Townswoman”). Sgraffita by Edmund Burke and Jan Zamoyski.

Cathedral of St.. John The Baptist zbudowana została w latach 1947-1954 according to the project by arch. Jan Zachwatowicz in cooperation with architects Stanisław Marzyński, Tadeusz Zagrodzki and Stanisław Hempel, which developed a reinforced concrete structure. The building was built on the site of the blown up village 1944 year of the gothic church from the beginning of the 15th century, rebuilt in the first half of the 19th century in the then fashionable English Gothic style by arch. Adam Idźkowski. The current facade was composed in the style of the so-called. Brick Gothic Masovian, partly according to Idźkowski's inventory. The portal is a reconstruction (The door forged in copper, designed by Stanisław Marzyński, was made by Adam Jabłoński), The stone and sgraffito frieze was designed by Kazimierz Knothe according to the fragment found. Interior, equipped to 1973 year, adorns the pulpit (designed by Józef Trenarowski with 1959 year), stables (from years 1959-1961) they are a reconstruction of the damaged baroque stalls founded by King Jan III. The main altar is designed by A.. Jabłoński (with 1966 year), bishop's throne of the project arch. Jan Bogusławski (with 1966 year), stained glass designed by Wacław Taranczewski (before 1973 a year). Black marble baptismal font is from 1631 year (signed “Peter Noire the French”), epitaphs and tombstones from the 16th-17th centuries (among others, the tombstone of Masovian dukes from the first half of the 16th century, the work of Bernardino de Gianotis and Jan Cini). The reconstructed tombstone of St.. Małachowski is the work of the Danish sculptor Bertel Thorwaldsen. Among the chapels, the mausoleum of Primate Stefan Wyszyński with a marble sarcophagus draws attention (created in the years 1986-1987 according to the project by arch. Bolesław Szmidt), stained glass and mosaic designed by Zbigniew Łoskot. In the basement from the fourteenth to the twentieth century, there are, among others, crypts: President Gabriel Narutowicz (project arch. Marian Lalewicz), Henryk Sienkiewicz (project arch. Konstanty Jakimowicz from 1924 year). In the outer wall of the cathedral, from ul. Deanery, a track from a remote-controlled German mine tank was built “Goliath”, attacking the Old Town during the Warsaw Uprising 1944 year.