I love a good relaxing simulation game. I'm always down to try out a new Sims title, or a theme park builder, or--the newest established style in the genre--a career simulator. There's a meditative quality to even the most stressful releases in this genre. You are fully in control of an immersive world where anything that goes wrong can be fixed instantly with a reset.
My favorite among these have sandbox modes, where time and money are of no value and you can build whatever you want. The artificial scarcity of earning money in the regular modes isn't even that inconvenient, as the developers tend to be quite generous with funds compared to how city building or repair work would go in the real world. Still, I prefer a simulation with no firm deadlines, just clear objectives and a lot of creative freedom. That's almost like a sandbox mode, just with a few more critical elements to deal with.