Forget bullet trains. Slovakia wants to transport people through a tube at speeds of more than 700 miles an hour.

Hyperloop Transportation Technologies says it reached an agreement with Slovakia to explore building an ultra high-speed transit system known as a Hyperloop. The system, which would involve hurtling passengers or cargo in pods through a depressurized tube, could potentially connect European cities Bratislava, Vienna, and Budapest.

The current agreement, however, only includes Slovakia.

The 50 mile Bratislava-to-Vienna route would take an estimated eight minutes at full speed. Right now, it takes about an hour to drive between the two cities.

HTT CEO Dirk Ahlborn said in a statement that having a European Hyperloop presence will “incentivize collaboration and innovation within Slovakia and throughout Europe.” A rival startup in Los Angeles called Hyperloop Technologies is also working on the technology.

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Of course, Hyperloops are entirely a speculative idea—albeit an exciting one. Many challenges remain as to how HTT, or others pursuing the same goal, will develop this futuristic transportation system. The new technology, even if it works, could be slowed considerably by regulations.

The idea of a Hyperloop was first floated by SpaceX and Tesla CEO Elon Musk, who posted a white paper in 2013 describing a Hyperloop. Musk, who said he wouldn’t build the system, challenged others to pursue and potentially develop the concept.

How does the Hyperloop work?

The idea has both fascinated and inspired a growing contingent of startups to try and develop the idea—or at least invest in it. HTT and Hyperloop Technology premiered soon after followed by a recent SpaceX-sponsored pod design competition and positive comments by U.S. Transportation Secretary Anthony Foxx about his agency potentially making research funding available.