I am stuck on the Path Of The Shell in Myst Uru: Complete Chronicles?

I am stuck on the one level where you are on an island with a weird tower in the middle and you can switch in between the three versions of it without exiting the Linking Book. The space one, the normal one, and the one where you can only be in the boiler room. I have found a few of the Shell marks that you press like the 7 in the first path, but I am stuck on what to do. I have gotten to the boiler room like area. Please help!