As you can see from the timeline, the world-gates were built during The Golden Age (990 to 370 years ago).   They're always on, free to use, always publicly accessible (except during a military emergency such as the second battle of Ubaid).   Travel is between two gates, so you enter one and exit the equivalent gate in the other city.   As such, it takes about an hour to travel between Yonaguni and Balath using the world-gate system.