Actually the way it was discribed with events earlier is the easiest way to do it, it just takes a lot of set up and time.
If you want to make it quick, make one event first for the bridge, make sure it's got the two pages, the second page with "Always on top" checked, and set it's condition to say "Switch: 001 Bridge = ON". Thankfully ctrl+c and ctrl+v makes it a fairly short job of the rest, simply copy and past the event for the size of the bridge you wish to use, and then change each graphic to the oppropriate one.
After that make a new event with the "on player touch" activated and have it turn "ON" the switch 001: Bridge and you will now be able to walk under it, make sure to set a 2nd page up with the condiditon for "Switch: 001 Bridge = ON" and make no modification to the 2nd page other than that. Simply copy and past the event to cover however long the pathway is under the bridge, and you'll now be able to walk under it!
To be able to walk back onto it, make another event. On the first page have "on player touch" checked with the condiditon for "Switch: 001 Bridge = ON." Make the event turn the Switch: 001 Bridge = OFF. Place the event in front of the bridge and copy and past it to cover the width of the bridge.
For a visual of what this might look like..
Hope that's helpful to answering what you need done. The whole setup there took about 3 minutes to make, so it's not really too complicated. Just be sure to have the right events and switches in the right place or you'll get some odd bugs.