An underground railway, as the name says, is simply an railway which runs underground. They are also called subway or metro or even rapid transit or mass rapid transit (MRT). The last term tells more about the basic rules of the underground: it is a kind of urban transport system, and the city is the reason why it is underground. The ground on the surface is much too expensive, and probably there is no way to buy enough space for a tram, because it is full of buildings. Trams on the surface need at least some space on the road and thus increase traffic. Subways have their own rails and stations, do not influence surface traffic and are never delayed by surface traffic jams. So the underground has a high capacity and frequency of service, and a high grade of separation from other traffic.
The first underground was built in London, which was the biggest and most overcrowded city of the world in the mid 19th century. And also it was rich enough, people could afford the fee to repay the investment. And as a matter of fact the railway and the construction of deep tunnels was both developed in England.
The next underground which was built was in Budapest, Hungary, the first underground on the continent. And now the underground fever started in the big cities, and one after the other built its own system. Today 162 cities have rapid transit systems, totalling more than 8,000km track and 7,000 stations.
We are not able or willing to list all subways of the world. Actually there are specialized websites for that too. But we want to list those of special touristic interest. Some of the subways are actually underground design or art orgies, some are called "the longest art galley of the world". Others have technical specialties which make them quite interesting. So you will find subways on showcaves.com which are worth a visit, not simply for getting from one place to another, but to spend time there and do sme sightseeing. And its actually a pretty cheap visit, as in most countries the fee for a subway ticket is much lower than the entrance fee to a museum or show cave.
|10-JAN-1863||Metropolitan Railway opened, now part of the London Underground.|
|1890||City & South London Railway opened, now part of the London Underground.|
|02-MAY-1896||Budapesti metró (Budapest Metro) opened.|
|14-DEC-1896||Glasgow Subway opened.|
|1897||Green Line in Boston opened.|
|1900||Métro de Paris (Paris Métro) opened.|
|1902||U-Bahn in Berlin opened.|
|2002||Copenhagen Metro opened.|