The 38-meter (125-feet) stainless steel slide has a gradient of up to 34 degrees. The council in Estepona, in southern Spain, advertised it as a useful fast way of getting between two streets which could be used by people of any age.
But video posted on social media showed one user hurtling down the slide and landing hard.
The council said it was an isolated incident and that hundreds of other users were unhurt. The slide remains closed Monday after being shut for a safety review Friday, a day after it opened.