Thunder Cart

The Kingdom of the Rising Sun and the Kingdom of the Elements are great allies who depend on one another for many many goods.  Their trading is so strong, war between them might be impossible for both would lose too many resources to fight a war.
Trade took many weeks in the days of walking between the two countries.  Now with the thunder carts, it takes a mare 8 hours.  In the Kingdom of the Elements, there are those who can move rock with magic, called Rock Spirits.  The rock spirits built a ramp, with a minuscule slope, which connects the two kingdoms.  The ramp travels over hundreds and hundreds of miles, stretching across the forest of Amma.  This ramp is huge, reaching high into the sky at its peak, starting near the mountain tops.
There is a ramp going each way, they carry Thunder carts, the size of cargo ships, and when they are rolled down the ramp hundreds of miles, picking up terrifying speed, they sound like rolling thunder.  coming to their destination going hundreds of miles an hour, the ramps at the end come to a sudden upward spike where the Thunder carts are launched upwards up almost perpendicular to the ground until the lose their momentum nearing the upper end.  The system has been protected so operators of the Thunder Ramps tie up the ship and hook it all uptight to the top of the ramp just as it comes to a stop, it does not fall it will stop suspended in the air by chains, and ropes galore.  
Once unloaded, it will be carefully shifted from the arriving ramp to the departing ramp, loaded with goods to be shipped to the other kingdom and sent on its merry way.  
Everywhere the thunder cart goes may be only two places, but it delivers goods that bring the people of their kingdoms much joy.  This trading system also employees thousands of people who feed their family each time a thunder cart pulls in.