This article may contain outdated information that is inaccurate for the current version of the game. It was last updated for 1.7.
Tourists can enter a city through many transportation types, but when you start a game, they will have access by the highway only. Tourists will visit all cities, but their numbers are decided by how attractive your city is. Attractiveness is raised by high land value and monuments. Land value can be increased by building parks and plazas, which also help zoned buildings in the city to level up.
As an example, when your city has produced 1000 units of goods, you gain the Stadium of Many Things. Upon reaching the goal, the Stadium becomes available in the menu and you can place it in your city. It's a popular location for many of your citizens, but also draws in tourists and increases happiness of citizens living near it. It's often a good idea to make sure monuments have good public transport connections, so roads around them don't get too busy.
Tourists also come to your city to see sights and shop. This can greatly increase your tax income, because tax is paid for every unit of goods sold. It also means that tourists want to get to your commercial areas and transportation should be designed to make it as easy as possible for them to do so. Tourists can come to the city by ship, airplane, train, the Space Elevator monument, or with their own car. For tourists that come in by means other than their own car, public transport is very important. The better tourists can get around, the more money they tend to spend in your city. The key is to earn and build monuments to draw in tourists, and then provide them with good transportation options inside the city to keep them there. Large amounts of tourists can also create traffic jams if they use their own cars instead of public transport, so you can avoid a lot of problems by giving them the means to move around easily.