Before the bridge over the river Don was built in Kintore, a ferry used to run across the river. Boatie Marnoch, or George Marnoch, was the last ferryman before the orginal bridge was built in 1882, and was a well known character around Kintore. The current bridge was built in 1986.
Access to the cache is likely easiest by parking on the street at the co-ordinates below and walking over the railway level crossing towards the bridge. You may be able to find a closer spot to the cache to stop at if the road is quiet. A little bit of stealth may be required, a lot of fishing muggles access the river around this bridge.