Sayyidina Jabir bin Abdullah (RA) said, “We used to say (الله أكبر) Allahu Akbar when we went up a high place and Subhanallah   (سبحان الله ) when we went down a valley.” (Bukhari) One of the wisdoms of saying (الله أكبر) Allahu Akbar when going upwards is that one is always reminded that no matter how high he reaches, Allah is the Greatest and Highest. When going downwards, one says SubhaanAllah (سبحان الله ) to recall that Allah is free from all faults and He can never be lowered.