Knapsack Viaduct: A Bridge Through Time
Knapsack Viaduct: A Bridge Through Time
If you’ve ever wandered the bush trails around Glenbrook, you’ll know there’s something quietly powerful about the way nature and history live side by side here. Among the dry eucalypts and sandstone, you’ll find old stone bridges that once carried the weight of steam trains and horse-drawn carts — structures that have stood for over a century, still holding strong.
This walk takes you through two of the Blue Mountains’ most remarkable pieces of engineering history: Lennox Bridge and Knapsack Viaduct. Built decades apart, they each tell a story of grit, craftsmanship, and the ever-changing ways people have crossed this rugged landscape.
It’s a hike that’s not just about getting from A to B — it’s about pausing under arches built by hand, running your fingers along old stonework, and realising just how many footsteps came before yours.
Quick Details
Length: Approx. 4km loop
Elevation: Around 100m of gentle climbing
Grade: Easy
Best season: Year-round, but spring and autumn are particularly lovely
Suitable for kids: Yes
Starting the Trail
I was on my own this week for a solo hike in the lower Blue Mountains area and settled on a wander around Knapsack reserve. After parking by Lennox Bridge, there were already a few people down by the bridge, so I decided to save it for the end of the walk. I headed off on the Old Mitchells Pass trail before shortly taking a sharp left, up a flight of stairs. The sounds of the people below me at the bridge gave way to the quiet sounds of the wind through the trees, as I followed the wide dirt track through the bush.
Marges Lookout
After only 600m, I reached Marges Lookout, which offers wide views over the lower Blue Mountains and Western Sydney. It’s not the most dramatic lookout in the Mountains, but it’s a lovely spot for a breather — especially in the cooler months, when the air is crisp and clear. You really get the sense of standing on the border of two worlds. The wild mountains on one side, the urban sprawl on the other.
Elizabeth Lookout
I turned around and followed the wide fire trail behind me, charmingly named “Lovers Walk” — though why it’s called that, I’ve got no idea. A few small foot tracks branched off toward the next lookout, but I wasn’t in a rush. Since this wasn’t going to be a long hike, I stayed on the main trail. Soon, I came to a junction and turned left onto another wide fire trail. It’s actually marked as a road on the map, and wide enough to drive on — though I’ve never seen a car here.
About 1.3km into the hike, I reached Elizabeth Lookout. These are quiet spots, not crowded like the popular viewpoints further up the mountains, and that’s part of their charm. Often, you’ll have them entirely to yourself.
There’s an old covered seating area here, perfect for a family picnic if you wanted. As the only food in my pack was a handful of muesli bars, I skipped the sit-down and kept going.
With my back towards the lookout, I took the track on my left, past one of the most amazing sign posts I’ve seen on a hiking trail in the Blue Mountains, and had to stop to look at it. I text Jess straight away to let her know we’ve been dressing all wrong for hikes. Apparently, the correct hiking attire involves a dress and bonnet. Who knew?
Knapsack Viaduct
I wandered down a sandstone staircase, and along a wide track that gently winds down the hill—still texting Jess that we should turn that sign into a t-shirt. The trail hugs the slope, and before long, the golden arches of Knapsack Viaduct appeared ahead, framed by trees like a cathedral in the forest. As I got closer, I took an unmarked foot track down the hill to reach the base of the sandstone pillars.
Built in the 1860s as part of the original Great Western Railway, the viaduct was an ambitious solution to the monumental challenge of climbing the Blue Mountains by train. Seven elegant sandstone arches span the gully, crafted by hand and shaped by convict labour. For decades, steam trains rumbled over them, pushing westward into the mountains.
Later, it was widened to carry cars as part of the Great Western Highway. From railway to roadway — it adapted with the times. Eventually, a newer road bypassed it altogether, and the viaduct was quietly retired from transport duties in the 1990s. Now it stands peacefully in the bush, a beautiful reminder of how human engineering can age gracefully into the landscape.
I climbed back up to the top of the bridge and crossed it. From up there, you get another expansive view of the valley — and of the newer viaduct that replaced this one when the railway was realigned. At the far end, a steep track leads up to Sidings Lookout. I’ve been up before — the views are okay, but similar to Marges and Elizabeth. I gave it a miss this time.
The Old Great Western Highway
This section of the track is paved and mostly flat - leading from the viaduct to a carpark area about 1km away. This used to be a roadway, but is now just a footpath and cycling track. It’s pleasant enough and wandering along I couldn’t help but wonder what it must have been like to drive through here back when this path was a road for cars.
Just before you reach the Knapsack car park area there’s a track heading up the hill to the left, that’s signposted, to take you back to Marges lookout and Lennox Bridge. Unfortunately there’s no pedestrian access along the bitumen road between Knapsack car park and Lennox Bridge. The track is steep, but nothing unmanageable. I soon reached the bridge, and this time I was the only visitor. I crossed over the bridge to reach the staircase on the other side to walk down to the base.
Lennox Bridge
In the early 1800s the road leading up the Blue Mountains was rough and dangerous, especially when it crossed Lapstone Creek. David Lennox, a Scottish stonemason and convict, designed a single-span stone arch to solve the problem. He used locally quarried sandstone and a construction technique that relied on precise geometry rather than mortar — the stones hold each other in place through sheer craftsmanship and pressure.
The result? A perfectly curved bridge that’s still standing strong nearly 200 years later. It’s a quiet place these days, tucked beneath tall trees and often dappled in morning light, but it carries the weight of history with every block of sandstone. When you walk across it, you’re walking on one of the earliest pieces of civil engineering in New South Wales. A bridge built with hand tools, muscle, and know-how — a reminder that there’s a gentle beauty in infrastructure built for its surroundings, not in spite of them.
Getting There
Knapsack Reserve can be found in Glenbrook in the lower Blue Mountains, a short drive from Sydney. Turn off the Great Western Highway at Blaxland McDonalds, onto Layton Avenue. You’ll drive under a bridge, and through a roundabout, onto Mitchells Pass. At the bottom of the hill, you turn left onto a narrower street (still Mitchells Pass), which soon brings you to Lennox Bridge. All roads are sign posted.
Tips and Tricks
You can drive over Lennox bridge, and drive further down the road to Knapsack Reserve car park if you’d prefer to skip the in-between sections and just hike around the Viaduct and bridge.
Most of the tracks around the reserve are signposted, but not all are. Having a map of the area handy will help to not get lost.
Knapsack Reserve is a popular area for bike riders, so consider swapping the hiking boots for a mountain bike.