in olivine city you can get strenght.....make sure that you have geodude or any pokemon that will be able to learn that HM......in the pokemon center...you can see their a house,,left on it.....go inside....it is a cofee shop of the sailors....at the last table there was a man...talk to him.....and he will give you that HM.......
use strength
In Pokémon Crystal, to move the boulders in the Cianwood Gym, you'll need the move Strength. First, you must obtain the HM04 (Strength) from a man in the Olivine Lighthouse. After teaching it to one of your Pokémon, you can then push the boulders around the gym to create a path to reach the gym leader, Chuck. Remember to solve the puzzles by pushing the boulders in the correct order to clear your way!
Your Pokemon are supposed to learn strength and move the boulders to the wholes.
The 5th Gym is in Cianwood City.
you go to olivine then battle jasmine
you have to get strength
Outside Cianwood City Gym.
Talk to the woman outside the Cianwood City Gym.
The 5th Gym is in Cianwood City in Pokemon Silver, Gold, and Crystal.
You cannot as rock smash was not introduced until Gold/Silver/Crystal. You can use HM 04 Strength to move certain boulders though.
Push the boulders through the holes by using strength, then go down a hole yourself. Now it is possible to get to the land in the middle of the ice.
The 5th Gym is in Cianwood City in Pokemon Gold, Silver, and Crystal.