The only relevant notes are the ones that say turns ___ corner. They direct you close to the center. Reaching the center in less than 190 steps allows you to go to the second floor. To reach the 3rd floor you must use flash and to reach the fourth floor you must use strength. However, the only thing on the 2nd, 3rd, and 4th floors are money related items. After you get the plates from the first floor, you don't need to return unless you need lots of money.
Note: 14 of the 16 plates are on the first floor. The other 2 are given to you on route 13 (BW) or Undella Bay (BW2) by a man. I recommend you look at the source for more in depth information.
Source: Abyssal Ruins
Simple version: The turning corners refers to the intersection where there are 2 paths to choose. Turn on the 2nd, 3rd, 5th, and 7th intersections that you come to and go straight on the rest.