Railway Empire 2
71 Achievements
1,350
PC
Right through the middle
Build a tunnel
15
23.2%
How to unlock the Right through the middle achievement in Railway Empire 2 - Definitive Guide
The tracks you build can only be so steep, so at one point the builder will automatically pick a tunnel if your two lay points, when laying track, are far apart.
If you want to aim for this specifically, the US map has hills to the west of Boston, or to the west of Washington, which will easily suggest tunnels if trying to build a line from one side of the mountain to the other - they're not cheap but you can save/load before/after doing so... also if you're building track outside of cities (which these mountains are) the tracks don't actually need to go anywhere, so you can do just this tunnel and press Y to confirm build.
If you want to aim for this specifically, the US map has hills to the west of Boston, or to the west of Washington, which will easily suggest tunnels if trying to build a line from one side of the mountain to the other - they're not cheap but you can save/load before/after doing so... also if you're building track outside of cities (which these mountains are) the tracks don't actually need to go anywhere, so you can do just this tunnel and press Y to confirm build.