The old winch

at Denver Sluice, no longer in use if you hadn't guessed. The line would go from the winch, through the hole in the wall, then at right angles to be attached to a boat to be lowered down the slipway slope to the water, or hauled out. Beefy all-wheel drive vehicles now do the job instead. 

The line has made grooves at the edge of the hole in the wall.