Find great value on Frontier Airlines flights from BIL to DEN when you book with CheapOair! With Rocky Mountains on one side and Great Plains on the other, Denver couldn't have asked for a better setting. The greatest thing about Denver is that it offers a lot to do and explore for people of all ages. Start your vacation with a visit to the Red Rocks Park which offers many exciting hiking trails that will certainly challenge your limits. Watch exciting Broadway musicals and theatre productions at the Denver Center for the Performing Arts. Looking for family entertainment? Then head to the Elitch Gardens Amusement Park which offers many exciting rides and attractions.