Clue: Set up a route regularly crossing one continent or two (7)
Answer: EURASIA
Explanation: Definition: two
Reverse of A + alternate letters or RoUtE "crossing" or contaning I (one) SA (South America – one continent); Eurasia is geologically a single continent but historically regarded as two, so it would be nice to include "one continent or" in the definition, but that would mean the words were doing double duty