Well, there are at least two ways.
If you want a specific level to open a specific thing, I have a 'command' run after winning that can deactivate gates or activate bridges.
If you want winning any adventure to activate the first gate, than any adventure to activate the second...
well, that, I just have the win command set to copy/paste to place turtles in a somewhat long path that has a button/general command, then water tile, then button/general command, (Etc.).
Take this map as such.
xxxxxxx ------ x=wall
Bxxxxxx ----- B=button/gc
Wxxxxxx ----- W=Water logic
Bxxxxxx ----- P=Where to paste; Beats me what happens if something else is there...

PxCxxxx ----- C=What to copy - in this case, the dragon turtle.
B/P/C also have floor logic.
That's how I do it; I extend it for if I want more.
Not sure if that's the easiest way to do it, though...
that's just my way.
P.S. Copy/paste is CMD = 41, Xcopy coordinate, Ycopy coord, Xpaste coord, Ypaste coord.
and activate/deactivate/toggle is 1/2/3, respectfully.
