Detroit Metropolitan Wayne County Airport (DTW) is the major gateway, in Romulus about 20 miles southwest of downtown. It is a Delta hub with direct flights from across the United States, Europe, and Asia. The McNamara Terminal's interior light tunnel between concourses is itself worth a few minutes. A taxi to downtown runs around $50; SMART bus 261 is the cheap option.
Coleman A. Young International Airport (DET) in the city handles general aviation and a few small commercial flights.
Detroit is well-positioned for road travel: I-94 runs east to Chicago and west to Port Huron, I-75 runs south to Toledo and north to the Mackinac Bridge, and the Ambassador Bridge and Detroit-Windsor Tunnel both cross into Canada. From Toronto it is about four hours by car. The Amtrak Wolverine line connects Detroit to Chicago via Ann Arbor.