This is in an area known as Hilsea Lines. See link. https://en.m.wikipedia.org/wiki/Hilsea_Lines
There were 6 Bastions. Some have been repurposed but this one has been taken over by party goers and graffiti artists. It is overgrown and lots of detritus all around. Nonetheless it is a fascinating place to visit.
My Step daughter Lucy gave me an “educational tour”.
You've shown the combination of heritage and modern so well. There's street art and there's graffiti - this doesn't seem to add much to the surrounds, except a social comment which is probably not very complimentary. Sorry about the long comment - but I hate seeing heritage areas unappreciated. :)