Buy a turnkey rental property
Certain companies specialize in selling turnkey rental properties. These rentals require little to no work after buying -- this is a passive investment mostly for cash flow. (Of course, no rental is completely passive; you may have to get involved if things take an unexpected turn.)
In most circumstances, the properties have been renovated, have an existing tenant in place, and have a third-party management company handling the landlord responsibilities.
However, just because it’s a turnkey investment doesn’t mean it’s a worthwhile one. Research the market to determine if the purchase price, rental rate, and location of the property support the investment.