Rio Grande Games RIO564 Underwater Cities is a game for 2 to 4 players that takes about 30 minutes to play. In the game, players are merchants trying to build the best city under the sea. The game includes a board, a set of tiles, and a set of cards. The board is divided into four quadrants, each with its own color. The tiles are used to create the cityscape, and the cards are used to determine the resources available to the players. The players start the game with a set of five tiles, and each turn they can either place a tile on the board, take one from the stock, or use one of their two action cards to do something. The players can trade resources with each other, build new buildings, and research new technologies. The goal of the game is to build the best city possible, and the player with the most points at the end of the game wins.