Dead red nettle which flowers at this time of year isn’t actually a nettle, though it does look a bit like a nettle. It is visibly not dead either; that bit of the name just means it doesn’t sting. It doesn’t sting because it isn’t a nettle.
These plants were growing in various beds in the Castle Grounds Park, Bridgnorth. They were possibly uninvited visitors rather than official plantings, but none the worse for that.