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Listed buildings and structures are officially designated as being of special architectural, historical or cultural significance. There are over half a million listed structures in the United Kingdom, covered by around 375,000 listings.
Listed status is more commonly associated with buildings or groups of buildings, however it can cover many other structures, including bridges, headstones, steps, ponds, monuments, walls, phone boxes, wrecks, parks, and heritage sites, and in more recent times a road crossing (Abbey Road) and graffiti art (Banksy 'Spy-booth') have been included.

In England and Wales there are three main listing designations;
Grade I (2.5%) - exceptional interest, sometimes considered to be internationally important.
Grade II* (5.5%) - particularly important buildings of more than special interest.
Grade II (92%) - nationally important and of special interest.

There are also locally listed structures (at the discretion of local authorities) using A, B and C designations.

In Scotland three classifications are also used but the criteria are different. There are around 47,500 Listed buildings.
Category A (8%)- generally equivalent to Grade I and II* in England and Wales
Category B (51%)- this appears generally to cover the ground of Grade II, recognising national importance.
Category C (41%)- buildings of local importance, probably with some overlap with English Grade II.

In Northern Ireland the criteria are similar to Scotland, but the classifications are:
Grade A (2.3%)
Grade B+ (4.7%)
Grade B (93%)

Read more at Wikipedia Link

Kelham Island is one of Sheffield's eleven designated Quarters. Formerly an industrial area, the island itself was created by the building of a mill race, fed from the River Don to serve the water wheels powering the workshops of the areas' industrial heyday. The quarter was named after the island, however, the boundaries extend beyond the physical island created by the river and race.

The Quarter is roughly diamond in shape, and is bordered by Shalesmoor and Gibraltar Street to the south-west; Corporation Street to the south-east; Mowbray Street, Harvest Lane and Neepsend Lane to the north-east, and Ball Street and Cornish Street to the north-west. Green Lane and Alma Street form the main spine roads of the area. The Green Lane Works (Grade II* listed) and the Brooklyn Works (Grade II listed) are both important industrial heritage sites. A great deal of urban regeneration is evident in this area, as residential and social uses are mixed into this former industrial area.
The area is home to an industrial museum, the Kelham Island Museum, including the famous River Don Engine. The Chimney House for events and occasions and five pubs: the Kelham Island Tavern (twice CAMRA National Pub of the Year), the Fat Cat, The Wellington, the Ship Inn and The Milestone. It is also host to the Kelham Island Brewery (brewers of Pale Rider, amongst others).