Underneath the M4 Severn Bridge you’ll find a hidden world.

Car free walking routes make plenty of sense, especially when you travel by train and have a station to train station walking route to follow. This walk from Severn Tunnel Junction station to Chepstow station is part of the Wales Coast Path (Llwybr Arfordir Cymru) but it’s definitely a route with a difference.

For a start, you’ll be walking right underneath the M4 Prince of Wales Bridge.

Jump to the walking route

Whether you’re in England or Wales, the Severn Estuary is a fascinating place to be. From Severn Tunnel Junction station trains to England run deep underneath the water, and both the older Severn Bridge and the newer Prince of Wales Bridge carry motorway traffic.

You’ll get to see both bridges as well as the tunnel pumping station if you follow this walk on the Welsh side, but this walking route doesn’t cross back over into England.

If you do want to do that, you can add on a walk across the older Severn Bridge. 

Walking along the Severn Estuary

When you think of the Wales Coast Path, you probably don’t imagine the flat eerie landscape of the Gwent Levels. Or footpaths that take you alongside motorways. Or giant man-made bridges.

But for me, it’s the uniqueness of these experiences that keeps drawing me back to the Severn Estuary.

Across the water you can walk from Severn Beach station to both estuary bridges (the footpath on the English side is currently being updated alongside flood defences). But on the Welsh side, the footpath, isn’t as managed and you’ll meet less people.

Check out the footpath closures on the English side of the Severn Estuary.

That doesn’t mean that it’s quiet.

Quite the opposite in fact. At no point in my journey was I away from the sound of traffic but for me, that was part of the adventure. I love walking in places other people might not, especially when my walk takes me to locations I have only previously looked at from the car or train.

I’ve often wondered what it would be like to walk along the Severn’s tidal hinterland. And now I know.

The first sections of my walk were easy going under foot. With a combination of lanes, footpaths and grassy dykes, all was great until I turned inland.

It was March.

We had had a lot of rain.

The mud was over the top of my boots!

How to plan a walking route with OS Maps.

The Wales Coast Path

Llwybr Arfordir Cymru or the Wales Coast Path runs all the way from Chepstow (Cas-Gwent) in the south to Chester (Caer) in the North. It’s 870 miles go through both the Pembrokeshire Coast National Park and Eryri Snowdonia National Park as well as circumnavigating the peaceful Llyn Peninsula and the Isle of Anglesey.

Look out for the shell and dragon’s tail symbol on the Wales Coast Path signs.

Severn Tunnel Junction station

Many people travel through Severn Tunnel Junction station on their way to and from Wales but I’m guessing few stop to explore around it.

The train ride through the Severn Tunnel is only exciting if you know where you are so I recommend looking at the map before you travel.

I don’t recommend reading about the thousands of gallons of water pumped out each day until after you travel.

The toilets, should you find yourself at this station for some time, are behind the ticket office. Take a coat, it’s a draughty place.

Visiting Chepstow

After my walk, I met a friend and took an extra day to explore Chepstow. We enjoyed walking along the river bank and over the Old Wye Bridge back into England.

Perched on cliffs over the tidal River Wye, Chepstow Castle is fabulous. I recommend taking advantage of the free audio tour on offer, it really brought the castle’s impressive history to life.

Even better than that. Cadw Cymru offer a two-for-one discount if you arrive by train.

From Chepstow you can follow a 6-mile section of the Wye Valley Walk to Tintern Abbey, another Cadw Cymru property. There are also buses between the two. From Tintern Abbey we enjoyed a shorter walk up to Brockweir and back.

Walking route Severn Tunnel Junction station to Chepstow station

• Start station – Severn Tunnel Junction
• Finish station – Chepstow
• Distance – 16.39 km
• Elevation – 165 m
• Time – 4 hrs 30 minutes
• Refreshments – Picnic areas at Sudbrook and Black Rock
• Toilets – STJ station, Welsh Street car park Chepstow

Walking route GPX – Severn Tunnel Junction station to Chepstow station

Alongside the M4

Leave Severn Tunnel Junction station via the car park and take the bridge back over the railway line. Just before the motorway bridge, turn left to follow the lane alongside first the M4 and then the railway.

Underbridging

Follow the Wales Coast Path signs to take the footbridge over the M4 and onto the estuary foreshore path. Pass back underneath the M4 at the Prince of Wales Bridge (recommended selfie spot) and continue along the foreshore path to Sudbrook.

There’s a spring in my tunnel

At Sudbrook follow the Wales Coast Path signs to divert away from the foreshore around Victorian Sudbrook Pumping Station, which still clears thousands of gallons of water from the Severn Tunnel every day.

Did you know the railway through the Severn Tunnel is electrified?

When it is open, you can visit the Tunnel Centre at Sudbrook to find out more about the ambitious Severn Tunnel project.

Before there were bridges

Rejoin the foreshore path and continue to Black Rock where a ferry (met by two steam trains) used to be the only way to cross the estuary. If you arrive in summer, you might still be lucky enough to spot lave net fishermen in search of sustainable low tide salmon.

Level head, level crossing

After Black Rock, follow the Wales Coast Path along the dyke until you reach a level crossing. You might need to take the inland path around Black Rock if the tide is super high. Cross the railway on the green light and enter the field on the other side. 

Fields and another bridge

Warning: After rain, the next section across fields can get very (over boot level) muddy.

Following the yellow-topped posts, cross the fields to Mathern. After exploring, leave the village to follow the Wales Coast Path underneath the original Severn Bridge that carries the M48.

You can walk onto the bridge from here, the views are amazing.

Another mile, another river

Follow the Wales Coast Path signs through the outskirts of Chepstow and up along the River Wye estuary. Just before the Old Wye Bridge, you’ll come to a bench that marks the start (or end) of the Wales Coast Path. It’s worth continuing over the bridge for great views of Chepstow Castle and then on to explore the castle itself.

Author’s walk

This is just one of my many UK train adventures. Feel free to enjoy the others as well.

Have you ever looked down from a road bridge and wondered what it would be like to walk below? I do it all the time and on this walk I got to find out.

I was surprised by how much of the walk was dominated by the Prince of Wales Bridge. I was super excited to pass underneath it and because of it’s bend, it seemed to follow me for ages afterwards.

I’ve become a big fan of ‘underbridging’.

The foreshore paths are really good but I should have anticipated the state of the route section across the fields up to Mathern. I walked in March and it had been raining for most of February.

The mud was over my boots and at one point I thought I was going to get stuck.

Having made it to Mathern and eaten lunch in the church porch, I decided to avoid the next set of fields and diverted up a lane to Bulwark. This did mean I missed out on walking beneath the original Severn Estuary bridge but I can go back and do that another time.

Chepstow station is conveniently close to the Wales Coast Path.