The simplest way to get from Duncan to Lake Cowichan is to drive Highway 18. It starts at the Trans-Canada Highway in Duncan and ends at Lake Cowichan, a distance of about 26 km, with no transfers and no ferry.
Driving Highway 18
Leave Duncan on the Trans-Canada Highway and turn onto Highway 18 following the signs for Lake Cowichan. The road is mostly straight and wide, rebuilt in 1970 to a better alignment, and the posted limit is 100 km/h on most of it. At the west end it meets Youbou Road at Lake Cowichan.
Put Lake Cowichan, BC into your map app if you want exact directions to a particular address in town. Offline maps are worth having in case coverage drops.
Check conditions before you go
DriveBC lists closures, roadworks and weather alerts. Heavy rain or snow can slow a trip in winter, so check in the morning if the forecast looks rough. Daylight helps on any rural stretch.
Without your own car
Transit in the Cowichan Valley is run by BC Transit. Whether a bus covers this particular trip, and how often, is best checked in the BC Transit trip planner for the Cowichan Valley, since schedules change. Do not assume a weekend service matches a weekday one.
A taxi is the direct option when the timing does not suit a bus. See Cowichan taxi for local service, and use the taxi fare estimator for a starting figure on the fare.
If you are arriving from the Lower Mainland or Victoria, the first job is reaching Duncan, which sits on the Trans-Canada Highway. From there the Lake Cowichan leg is short. Check the BC Ferries sailing schedule for the crossing, and expect the busiest sailings on summer weekends and holiday Fridays.
Lake Cowichan is a small town on the lake of the same name, so it is worth confirming where you are staying or meeting someone before you arrive. Parking near the waterfront can fill up on warm summer days, so a drop off may be easier than hunting for a space.