- Creates a passage underneath a Mountain. Units may use this passage to either move directly across the Mountain tile, or to any other valid land tile next to another Mountain Tunnel in the same mountain range.
- Trade Routes may also use the tunnel; they gain additional Gold for doing so.
- Costs 2 Movement.
- Can only be built on an adjacent Mountain tile.
- Cannot be pillaged or removed.
The Mountain Tunnel is one of the engineering projects built by Military Engineers to help you customize the environment around you to your will. This tile improvement (or its Incan equivalent, the Qhapaq Ñan) is useful whether in peace or war. You can put this improvement at two ends of a long range of mountains and let your units traverse the distance in just one turn, or just one tunnel in the middle to open a path through it so you do not have to waste time going around the mountain range. Whether the units we are talking about are civilian units, religious units or military units, no matter what their purpose is, this improvement helps collapse the map and bring distant regions much closer, as long as you can scope out a strategic mountain range for it. And, given the new map-generating algorithms in Gathering Storm which tend to produce long mountain ranges which lock out portions of the map, this improvement becomes really useful!
Also, Trade Routes going through Mountain Tunnels will have increased yields in Gold.
If you play as the Inca, there is no need to build this improvement - stick with the Qhapaq Ñan, as it is built by Builders and becomes available much earlier.
The very first tunnels date back thousands of years. These ancient underground routes covered a range of purposes from transporting water to providing tactical advantages to troops. Despite the challenges of this sort of excavation at the time, the Crypta Neapolitana tunnel near Naples, dating to 37 BC, measures 700 meters in length and nearly 10 meters high. It was also completed with ventilation shafts, and was still used as a roadway until the early 1900s.
Tunnel construction really began to boom as railroads became a popular means of transport, and brought with them very specific needs. The first railroad tunnel was completed in the United States in 1834 by means of black powder blasting at a rate of 18 inches per day. Today, tunnels are commonplace throughout the world as part of public transit systems.
Move a military unit into an enemy's owned tile using a Mountain Tunnel (or Qhapaq Nan)