In Blue Border, the players are divers who must play cards to dive to a certain depth, and then return to land. However, they must take care not to dive or come up too quickly.
The game centers around a deck of 32 cards, numbered 1 to 32 on the front, with various shades of blue on the back, corresponding to the number on the card.
On a player's turn, they can choose to play any one of five available cards to the next location in their dive, or can choose to pass. Players can only see the blue back side of the available cards. Once a player has determined a card to play, the other players may challenge that the card is within an acceptable range of cards to be played.
The first player to play 4 descending cards, reach a certain depth, and then 3 more cards to ascend, wins. The rules state that the other players should provide generous applause for the winner.