This is a picture of Heros' Square (Hősök tere) in Budapest.
The slide was one of a series of slides which show locations around Poland, and initially I thought this could be in Poland, but when I couldn't find anything which matched, and because a very helpful reader had pointed out that another slide was of a church in Budapest, I widened my search to that city and found it.
The picture itself is taken from quite a distance back and so shows the statue on a column as well as the archways of the structure. Although the slide isn't marked with a date, I believe this photo was taken in the 1960s, and the design of the coaches parked to the side seems to support that.