Unioninkatu (Swedish: Unionsgatan, both meaning "Union Street") is one of the key streets in the historic centre of Helsinki, Finland. It stretches from the Tähtitorninvuori hill to the Pitkäsilta bridge and is about 1.5 km long. Its southern part is located in Kaartinkaupunki up to the Esplanadi park, while the northern part acts as the border between Kruununhaka to the east and Kluuvi to the west. The street functions as a local assembly street.[1]
In the south, Unioninkatu is directly continued by the short street Kopernikuksentie leading to the gate of the Helsinki University Observatory. In the north, Unioninkatu is directly continued after the Pitkäsilta bridge by the street Siltasaarenkatu leading to the Kallio Church. Together these three streets form a 2.5 km long street line called Unioninakseli, the longest continuous straight street line in central Helsinki.
The northern end of Unioninkatu from the Kaisaniemi roundabout to Pitkäsilta is a busy traffic route, and forms a part of a road leading to Hakaniemi and then to Hämeentie together with Kaisaniemenkatu and Siltasaarenkatu. Many tram lines and all bus lines traveling from the Rautatientori square to the northern and northeastern parts of Helsinki and towards eastern Vantaa run along it. This part of Unioninkatu is a bit wider than the rest of the street and contains a gate leading to the Kaisaniemi botanical gardens.