I'm really liking "The High Line" project in New York City. The park is a great recycling of an disused urban space, in this case a railroad, to inject greenery and tranquility into the cityscape.
This elevated parkland, designed by studiosJames Corner Field Operations & Diller Scofidio + Renfro seamlessly snakes through the buildings of Manhattan for over twenty blocks, injecting the countryside into just a small vein of huge concrete, steel and glass landscape.
I especially like how the railway's heritage's has not been disturbed. The new architectural elements slip seamlessly between the old tracks & sidings without disturbance, whilst the planted areas seem to feel like they've been left to overgrow.
I wish there was more apparent consideration made to use disused space in this country, not only for public space but housing too, especially as you can't seem to travel anywhere without seeing a "new build" housing project, rather than refurbishments.