How do you get to joyous tower in Pokemon Red rescue?

First you must go to the solar tower or cave then find the keys. ( You don't need these for HM surf but you can get other rare HM's)

Go to F20 and you will se a HM disk surrounded by water, go through it. ( You need a water Pokemon or a flying Pokemon for this).

You've got surf, go and clear the dungeon, then a mini cartoon will run about a robbery.

Go to nothern range F25 and fight LatiOS. When you have beaten him it will go to another cartoon and LatiOS explains about his sister Latias. You can now go to pitfall valley.

Go to F25 and rescue her, clear the dungeon then you will see her.

Then they will thank you and join your team.

LatiOS is level 30 and Latias is level 28.

Now you can go to Joyous Tower.