"When we see a sign that says ‘Danger: Do Not Enter’, we understand that this is simply a shorthand way of saying ‘Leaving Protected Zone: Demonstrate Personal Accountability Beyond This Point'."
Jeff Chapman (aka Ninjalicious)
The most active Urban Exploring forum in the UK. The community is very friendly and welcoming to newcomers as well as more experienced explorers. I highly recommend you check this site out if you haven't already.
A friends web site that has a lot of content as well as a lot of background information on the hobby. This site was created due to the inspiration I got from this.
Regularly updated, this site packs a comprehensive list of sites, some of which no longer exist. A lot of asylums and hospitals too.
An incredibly well documented site purely based on the Asylums of the UK. Collaborated by some very dedicated individuals, everything you need to know and more is detailed here.