Prova detta:
SELECT *
FROM travels.destinations AS D
WHERE D.name LIKE '%act%' AND D.sold = 'N' AND D.active = '1'
ORDER BY CASE WHEN D.name REGEXP '^[a-zA-Z]*$' AND D.name LIKE 'act%' THEN 0
WHEN D.name REGEXP '^[a-zA-Z]*$' AND D.name LIKE '%act' THEN 1
WHEN D.name REGEXP '^[a-zA-Z]*$' AND D.name LIKE '%act%' THEN 2
ELSE 3
END,
D.name
LIMIT 10