Board Game Arena

The Tunnel card doesn't seem to do anything, I've never seen a face down card, and what would be the point if your opponents can't see your grid?
EDIT: I really hope it stays that way, a card you couldn't see would really spoil the game.

Someone has reported a similar bug, see https://boardgamearena.com/bug?id=238560
Check, if this bug report matches your experience and then vote (and comment) the existing bug report or create a new one.

I'm not sure if it's a bug or something i don't understand.

I guess the point is the two player do not get the same card to place on the board, but don’t know who got what. It adds uncertainty.

The card does not mean that players put the card on the board face down.