I would say para. Because para means "to" and the sentence is saying "my brother bought a bike to ride in the mountains"
What is your opinion about the works of Joan Miró?
Answer:
Jugaban
Corrías
Pescaba
Esquiábamos
Comía
Bebíais
Decía
Subían
Patinaba
Trabajabas
Caminabais
Abríamos
