The Brig o'Waithe is a small arched bridge that crosses the mouth of the Stenness Loch, a large sea loch in Orkney's West Mainland, as it outflows into the Bay of Ireland and Scapa Flow beyond. You'll pass over it if you're travelling to Stromness from the east, but it might be a 'blink and you'll miss it' moment.
It's well worth taking some time to stop at the small car park on the south side of the bridge, though. The Stenness Loch is the largest brackish lagoon in the UK and the area is a haven for wildlife. The Brig o'Waithe is a popular haunt for otters, and there have been lots of daytime sightings here in recent years. You can stay in your car and scan the small grassy island just off the shore. If you don't see otters here then there's a good chance you'll get a glimpse of a hauled-out harbour seal.
If you're not having any luck then carefully cross the main road and check out the area around the bridge and shore on the loch-side. Again, seals are often seen on the rocky outcrops in the loch.