OK, when I said 'obscure building,' I meant something of no great historical interest; at least for most people. Indeed, only its high asbestos content saved it from demolition!
It's the old Boiler House at Stannington Children's Sanatorium, which closed in 1984 and was demolished c.1992. Only some staff houses and old air raid shelters remain. Unlike Gateshead Asylum (not in Gateshead) down the road, it was bulldozed before the age of the digital camera, therefore it doesn't feature much on sites such as 'derelictPlaces.co.uk.'
You'll find some photos of it here, but you'll have to scroll down and down and down.
http://www.derelictplaces.co.uk/main/military-sites/21897-millitary-hospital-phillipson-sanitarium-tranwell.html
It's located about 3 miles SSW of Morpeth and you'll find it on Google Earth at:
55degrees 07'55.82"North, 1degrees 42'23.20"West. Elevation 108m Eye alt 228m