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Aldwych is a closed station on the London Underground, located in the City of Westminster in central London. It was opened in 1907 with the name Strand, after the street on which it is located, and was the terminus and only station on the short Piccadilly line branch from Holborn that was a relic of the merger of two railway schemes. The station building is close to the junction of Strand and Surrey Street, near Aldwych. During its lifetime, the branch was the subject of a number of unrealised extension proposals that would have seen the tunnels through the station extended southwards, usually to Waterloo.
Served by a shuttle train for most of their life and suffering from low passenger numbers, the station and branch were considered for closure several times. A weekday peak hours-only service survived until closure in 1994, when the cost of replacing the lifts was considered too high compared to the income generated.
Disused parts of the station and the running tunnels were used during both World Wars to shelter artworks from London's public galleries and museums from bombing.
The station has long been popular as a filming location and has appeared as itself and as other London Underground stations in a number of films. In recognition of its historical significance, the station is a Grade II listed building. Link

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