Skreelink is offering a bounty in order to fill out the trains hangar and outside location! This is the same location that was used for the trains contest two months ago. A few 40x12 plots have remained available, and he wants to see completed projects on each of them!

To visit this location and possibly build something, from Central, use the overworld Western Line to the desert branch (third stop). Once there, switch to the side line and disembark at the first stop! Alternatively, from Nether Central, use the West line, get out at the first substation (Alucard), then select the Canada line.

Here's what Skreelink has to say on this matter:

I'm paying a bounty to fill the train museum! There's two plots inside, two plots outside. Anyone that drops a train on a plot and leaves a note in my PO with their name, train name, and date completed earns 3 diamond blocks and 3 emerald blocks.