Utrecht is close to the junction ‘Oudenrijn. From which direction you come from, always keep The Hague (A12). Then take the exit (15) Montfoort and then via the N228 take the second exit (IJsselstein) left the North IJsseldijk on. After 1200 meters you will see on the right Marina Marnemoende.
Coming from The Hague (A12), can also take exit (15) Montfort.