Oracle Min - ORA-00937 not a single-group group function
You want to aggregate an aggregate, so the easiest way to see this is to group twice, I believe. You may also want to rename the subquery table aliases I've used here to make them more meaningful.

SELECT sub2_.bus, MIN(sub2_.fare), MIN(sub2_.dest)
  FROM (SELECT sub1_.bus, MIN(sub1_.fare) AS fare, sub1_.dest
          FROM (SELECT tickets.bus_id    AS bus,
                       tickets.fare      AS fare,
                       route.destination AS dest
                  FROM tickets
                  LEFT JOIN route
                    ON route.route_id = tickets.route_id) sub1_
         GROUP BY sub1_.bus, sub1_.dest
        HAVING COUNT(sub1_.bus) &gt; 1) sub2_
 GROUP BY sub2_.bus
HAVING COUNT(*) &gt; 1