In 1794, Rev. Alexander MacFarlane wrote in his Statistical Account of the parish of Kilfinan,
"On a rocky point on the coast of Loch Fyne about a mile below the church is to be seen the vestige of a building called Caisteal Mhic Eoghain, or Mac Ewen's castle"
In 1990, The Clan Ewen Society had a cairn erected among the ruins of Caisteal Mhic Eoghain near Kilfinan on the shores of Loch Fyne.
You can visit the cairn and the castle on foot today. The following description of the route from Kilfinan is by the writer and artist Michael Lidwell (I haven't been able to discover what book it appears in - any info gratefully received):
Length: 1.5 miles/2km; Height climbed negligible.
There is a large carpark at the hotel from which the way lies across the bridge and along to a group of restored cottages (Lindsaig cottage / The Old Smiddy). Turn down the access driveway then through a gate into a field. Fishing by permit only.
The route is signposted along the bank of the river and over stiles. There is a precarious suspension bridge across the river, which links to a path beside a lagoon formed behind the shingle beach and frequented by geese. From there a private road goes back to the main road past Otter House.
The riverside path crosses a ditch by a plank bridge then after another stile rises to a signpost on top of the bank. Walk along the shingle bank or coarse sands, according to the state of the tide for about ½ mile, while watching the gulls and sanderlings playing in the surf.
At the end of the beach cross a small burn on stepping stones and pass through another gate onto a very rough track, where there is another signpost. Cattle feeding in the shelter of a small cliff of weathered rocks and a grove of gnarled oaks have churned up the ground. So carefully pick your way along the shoreline or at a higher level across the rough pasture to the headland.
Here is a prominent pillar with a bronze plaque, placed on the edge of a stone circle outlined by the turf covered ruins. It offers a clear view down Loch Fyne and across Loch Gilp from a breezy spot.
When I was there myself recently, I approached from the entrance to Fearnoch and made my way past an ancient cairn to meet the main route along the beach (one of the footbridges was broken but it was easy enough to get across). At the end of the beach, a sign points up into the wood. Open the gate and keep on the same bearing as you head through the clearing and out the other side. As you come out through the trees, you'll see the ruins of the castle ahead visibly dominated by the presence of the cairn or pillar. On the way back, I followed the edge of the wood inland until it met the path back past the farmhouse at Fearnoch.
You should be able to find your way with no further preparation, but it's a good idea to drop in at the Hotel if it's open where they keep a visitor book and can help with local knowledge. If in doubt, I'd advise buying one of the Ordnance Survey maps which cover the area before you set off for Kilfinan (either Landranger 62 or better still, Explorer 362).