Valentine is remote by any measure. The nearest commercial airport with regular service is in Rapid City, South Dakota, about three hours north on US-83. Driving is the practical option for most visitors: US-83 runs north–south through town, intersecting US-20 (the east–west highway across the Sand Hills). From Omaha the drive is about four and a half hours; from Denver around five.
There is no intercity bus or train service to Valentine. Rent a car before you arrive — there is no car hire in town.