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An underground network is usefull to enlarge creation possibilities.
They can be a bit complicated tunnels or very complew underground networks such as a metro network.
Plus, metro is a solution to transport a lot of passengers through a city without modifying it.
Undersea tunnels can also be made, they are useful on not too long distances.
In the latest releases of Simutrans, there are two kinds of underground view. The first one show everything under the ground, it can be used by the shortcut “U”.
There is another useful view : the sliced view. It allows to see underground structures on only one level. It's convenient for underground construction. To use it, go in display options.
When you normaly build a tunnel, an underground way goes from a tunnel extremity straight to the other one.
To build a network, it would be more convenient to have only one tunnel entry. To build a tunnel entry, use the the tunnel tool when keeping ctrl key on.
To build underground ways then, the usual way tool won't be used as on the ground. You have to use the tunnel tool, the same which you built the tunnel entry with.
The underground ways have the same behaviour as over ground ones. You can build signals, stations, depots, you can electrify them … You can also build tram ways in road tunnels.
Underground slopes are a bit difficult to use. If you build a network with slopes, you should better use the sliced view.
If you want to build a down slope at the extremity of a way, you have to use the terrain modification tool.
That's the same for up slopes but because of the sliced view caracteristics, you should build your network from up to down.
Actually if you dig a bit you will see that it's possible to build under the sea level with a tunnel. It's by this way that undersea tunnels are built.
However be careful to the sea deepness. You won't build a tunnel at level -1 under a sea which is -3 deep.
On the other hand, you have to use the sliced view to see under the water.
Now you know everything about tunnels, the most twisted metros are yours ;)
