The Tunnel (1st edition)
General info and comments
- 4 land tiles
- 12 tunnel tokens, two tokens in six colors
The four land tiles are mixed with those of the basic game. Every player receives the tunnel tokens corresponding to his or her color. In games of two, each player may use three sets of tokens; in games with three players, each may use two sets. 
All the rules of the basic game apply, with the following additions.
Playing the Game
Claim tunnels with tokens
During his or her turn,  a player may place one of his or her tunnel tokens on any currently unclaimed  tunnel opening, including on the land tile which has just been placed. Independent of this, the rules for deploying a follower remain the same. 
When is an underground tunnel finished?
As long as there is no tunnel token claiming a tunnel opening, the road leading to it is "broken off," without being complete.  The road remains incomplete even when a tunnel token is placed on the tile. Only when the second tunnel token of the same color is placed on another unclaimed tunnel opening (which may or may not be on the same tile) are the tunnel "entrance" and "exit" defined, and the tunnel finished.  The road then runs underground through the tunnel, but is not completed at the tunnel exit. The road is completed in the usual way, such as by reaching a crossing.
The color of the tunnel tokens is only important for linking two tunnel openings. Indeed, the tunnel is built for everyone; for example, a thief of another color can score a road which goes through a finished tunnel. In extreme cases, a road may lead underground several times in a row. 
After scoring, the tunnel tokens remain where they are, so that at most five tunnels (or six with tunnels from other expansions) can be built.
Take care with the tiles shown beneath. 
Players may use tunnels in a cutthroat way to make a road impossible to complete and trap all the followers on it for the rest of the game: a player may lead to this situation by claiming a tunnel opening with a token and never placing the second token. This possibility has generated much debate.
In order to mitigate this situation, some variants have been suggested: 
- You are only allowed to place a tunnel token on a tunnel opening if at least 1 of your followers is placed on the road connected to that tunnel. (Thanks to Player77)
- The affected player is allowed to steal the 2nd tunnel token and place it immediately during their turn, if the token's owner did not use at least one opportunity to place it. (Thanks to Christwart Conrand, creator of the expansion)
- Both tunnel tokens must be placed at the same time when road with a tunnel is occupied by a player. Moreover, tunnel tokens should not be player-specific. (Thanks to Whaleyland)
- Players cannot use a tunnel token to block an opponent's follower. (Thanks to corinthiens13)
Tunnels in other expansions
Tiles from other expansions, such as The Princess and the Dragon and Abbey and the Mayor which also depict tunnels, can also be used with the rules for the Spielbox tunnel expansion; as such, the openings can be claimed with tokens. In this case the road leading through the tunnel does not count as continuous, contrary to the stated rules.
A player will get the Robber Baron tile if he or she places a tunnel token that completes the longest road at that moment in the game.
For Icons explanation and licensing please visit Icons page.
- For The Tunnel we have three sets of rules to draw on: those originally published in Spielbox; a set on Hans im Glück’s website; and, based on that, an English translation on the Spielbox website. We have used those of Hans im Glück as a basis for this section, although we will point out any differences between versions as necessary.
- The rules published in Spielbox say that in games of two, each may take two sets of chips.
- A specific time during the turn is not stated, indicating that the token can be placed at any time during the turn. (10/2014)
- The rules say "unoccupied", but we feel it is worth making a distinction between occupying (with a meeple) and claiming (with a token).
- This last sentence does not occur in the published Spielbox; it clarifies that a player may both deploy a follower and place a tunnel token in the same turn.
- This and the next section are greatly revised from the rules published in Spielbox, clarifying a number of issues.
- The rules only mention that the tunnel entrance and exit are "defined" but we feel it is worth making a distinction between a road being completed, and a tunnel being finished. The Spielbox English translation does not, and is potentially confusing.
- The Spielbox English rules add that a road may "[pass] behind other roads underground." We are inclined to think that this is a mistranslation of "hintereinander," or "in a row."
- It would seem logical that if the "entrance" and "exit" of a tunnel are on the same tile, they should only count as a single point for scoring, just as two segments of a city on a single tile only count as 1 tile for scoring purposes.
- Although not specifically stated, the finished road with tunnel tokens is scored during the normal scoring phase, as the rules do not indicate anything to the contrary. (10/2014)
This clarification was confirmed by Christwart Conrad, the author of the expansion. He confirmed the RRRR tile has 3 field segments.
He also provided a link to BGG discussing the fields on the four tiles.
The first two variants were discussed on two consecutive posts available on BGG:
The remaining variants where discussed on several posts on Carcassonne Central (replies #2 and #10):