I found this place one day while just walking past, and what a pleasant surprise. None of it is big: the centre itself only has a few rooms, including a classroom where they teach sessions for local schools. Around that is a nature reserve, which is also known as Gillespie Park. There are gardens, and tiny pockets of wood and grassland habitats. In among it all you'll also find artworks, including several in reclaimed scrap metal, and some carved stone seats. There's water reclamation pools (not at all smelly like you might think) and a huge wind turbine (which is a lot quieter than the passing trains)
It's only very small, so perhaps not a place to travel to see. But if you are in the area why not drop in.
There is more information at: http://www.islington.gov.uk/Contact/visitingoffices/ecologycentre.asp read more