A 20-tonne bridge is being hauled into place by hand because its remote location makes it impossible to use a crane.
The new bridge across Bracklinn Falls, near Callander, is expected to be fully in place by Sunday.
The wood and copper structure had to be built on site as the thick woodland also meant helicopters could not be used in the construction.
The original steel bridge was washed away by floods in August 2004.
Very heavy rain in that month also destroyed bridges in nearby Braeleny and Edinample, near Lochearnhead.
Kenny Auld, from Loch Lomond and the Trossachs National Park, said building the £110,000 bridge had been an "exceptionally difficult task".
"It's a 20m span across a very deep gorge," he said.
"For the last six years the community and the national park have been trying to get a replacement in place.
"I've taken three batches of Royal Engineers to the site and they've just laughed in my face and told me I'm crazy."
The national park had to build a small access road to the site to transport materials, but it is only accessible to four-wheel drives or quad bikes.
Engineers from Crief-based Strong Bridges built temporary steel rails across the gorge and mounted the bridge on skids so it could be pulled across.
"There's a hand winch on the other side with one or two people winching the 20 tonne bridge across," said Mr Auld, who is managing the project for the national park.
The bridge is made from Douglas firs from the Heritage Plantation in Dunkeld and has a copper roof.
When in place, it will give an "iconic view" of the falls, Mr Auld said.
The project has been funded by the national park, the Forth Valley and Lomond Leader and Scottish Natural Heritage and was built in partnership with Callander Community Development Trust.
The trust's John Snodin said people in Callander had lobbied for a new bridge ever since the old one was washed away six years ago.
"Both locals and tourists visit the site daily and the new bridge will be a destination in itself as well as a position to view the cataracts, which are impressive.
"The bridge is only a short distance from the car park but it can also be utilised to create a series of longer circuits in the Callander area."
It will be officially opened in November after landscaping and footpath work has been completed.