These submerged subway innovations show how much public transportation has advanced over time.

Though perhaps not the most desirable means of getting around town, subways typically offer civilians an affordable way to get from point A to point B. With innovations in terms of marketing stunts, the design of the actual trains and the way in which these spaces have become somewhat of a showcase for art, there's no telling where the future of subways may lie. Many of these public transit systems exist throughout the world, and many variations exist, making them an interesting public service to contrast and compare.

Though perhaps not as reliable as some might expect, subways are an inevitable component to most large cities, and increasingly, are being used as hubs for innovation.