Central Wisconsin Airport: The only practical airport for Wausau, 12 miles south of downtown. Rent a car at the airport; it is roughly a 20-minute drive and is far more reliable than trying to piece together rideshare in a small regional market. A taxi/rideshare, when available, is roughly a US$30–45 one-way proposition. CWA has service via Detroit, Minneapolis and Chicago O’Hare.
Lamers Bus Lines / Greyhound intercity service: There is daily bus service to and from Milwaukee via the Fox Valley, bookable through Greyhound and sometimes Amtrak when paired with a rail leg. It is useful if you are car-free and patient, but not a substitute for a train: Wausau has no passenger-rail station. Confirm the current stop and timetable before committing to a connection.
Wausau Downtown Airport: General aviation only; useful for private aircraft, not scheduled commercial arrivals.