Walk to the edge on the glen side and Glen Croe runs away south-east below you: steep grass on the left, plantation forest on the right, and a narrow single-track road doing a hairpin right under the car park before wandering down the middle of the glen. That's the Old Military Road, pushed through here by soldiers in the middle of the eighteenth century, after the Jacobite risings, so troops could be moved around the Highlands. The climb out of the glen was so long and steep that travellers got into the habit of stopping at the top to rest and be thankful, and the soldiers carved the words into a stone at the summit. The original stone is long gone, but its replacement stands at the bottom of the car park where the old road comes in, and you can still make out the lettering recording the road's repair by the 93rd Regiment in 1768 and its handover to the road commissioners in 1814. Johnson and Boswell came over the pass in 1773, and Wordsworth walked it with his sister Dorothy in 1803 and later wrote a sonnet about it.
The road you drove up was built in the late 1930s on the slope above the old one, and the old road hasn't retired. This pass gets landslides after heavy rain, and when they close the A83 the military road below you gets pressed back into service as the diversion.
For the photo, get the hairpin of old road in the bottom of the frame and let it lead the eye down the glen. It gives the slopes their scale.