You collect matching coloured cards to claim railway routes across the map. It gets pretty tense when someone takes the exact path you needed to connect your cities. We usually pull this out when we have a few friends over for some drinks. It is basically a staple for our regular weekend tabletop sessions at the pub. Just remember to not take the backstabbing too seriously when things get heated. The rules are straightforward enough so you can explain it to your neighbour in five minutes.