Lost Cities is a card game in Kosmos's two-player series. Initially, the game included a single deck of cards with values from 2 to 10 in five different colors, with three special "handshakes" ("HS" in the scoring examples below) in each color. Since 2018, the game includes six colorful colors, with the sixth color being optional for gameplay. A board is included to organize the discarded cards and help players organize their collections.

The goal of the game is to earn points through profitable archaeological expeditions at various locations represented by the colorful card colors. In each round, players must first play a card, either on an expedition or by discarding it to the appropriate discard pile, and then draw a card, either from the deck or from the top of a discard pile. Cards played on expeditions must be in ascending order but do not need to be consecutive. Handshakes are considered lower than 2 and represent investments in an expedition.

The game continues with players alternating turns until the last card is drawn from the deck. The remaining cards in players' hands are discarded, and players score their expeditions. Each expedition with at least one card played must be scored. Cards played on an expedition are worth points according to their value, while handshakes count as multipliers on the final total score. One handshake doubles the value of an expedition, two handshakes triple it, and three quadruple it. Expeditions start with a value of -20, so at least 20 points worth of cards must be played to be profitable.

Scoring examples follow:

• Scoring Example 1: An expedition has 2, 3, 7, 8, 10 for a total value of 30. This expedition is worth 10 total points: 30 plus the initial -20.
• Scoring Example 2: An expedition has 2 HS, and 4, 5, 6, 7, 8, 10 for a total value of 40. This expedition is worth 80 total points: 40 points for the cards, plus the initial -20, ×3 for the two multipliers, plus the 20-point bonus for playing 8+ cards.
• Scoring Example 3: An expedition has 1 HS, and 4, 6, 7 for a total value of 17. This expedition is worth -6 total points: 17 plus the initial -20, ×2 for the multiplier.