The standard approach is via the Lena Lake Trailhead. Driving north on Highway 101 about 13.5 miles north of the town of Hoodsport, WA turn left on Hamma Hamma River Forest Service Road 25. The road is well signed and the trailhead is about 7.7 miles from Highway 101 to the Lena Lake Trailhead. The parking area, as large as it is, is often over crowded but most will be here for Lena Lake. Take the Lena Lake trail and hike the wide, well graded trail for about 3 miles. Shortly before Lena Lake, find the trail marked for Upper Lena Lake on the left and continue on towards Upper Lena Lake. The trail begins to steepen here and does not let up much until you reach Upper Lena Lake. Distance and elevation from trailhead to Upper Lena Lake is about 7 miles 3900 ft elevation one way.
An alternate route could be achieved via the Putvin Trailhead. Where the Putvin trail makes the final crossing of an abandoned logging road to head to Lake of the Angels (see Mt. Stone) keep heading east on the road and create your own route as you cross the washout created by Boulder Creek to gain access to Bretherton's south ridge which is hidden by dense forest at this elevation. I'm unsure what would motivate someone to take this approach, but it is worth mentioning. The vast majority of summiters will use the Upper Lena Lake route.
To park at the Lena Lake Trailhead, you will either need a Northwest Forest Pass or an Interagency America the Beautiful Pass
which can be purchased online or at any National Park or Forest Service Ranger Station.
For overnight camping in Olympic National Park, you will need to pay a Wilderness Use Fee for a permit which you must display on your tent. The permits are required from May 1 through September 30. The fee is $5 to register and then $2 per person per night. Another option is to get an annual pass for $30 (then $15 for each additional household member). The permits can be picked up at the following ranger stations:
Main Wilderness Information Center (WIC) in Port Angeles in person or by phone. The WIC is located within the Olympic National Park Visitor Center. Phone: (360) 565-3100
Quinault Wilderness Information Center located at the South Shore Lake Quinault Forest Service Ranger Station. Phone: (360) 288-0232
Olympic National Park/Olympic National Forest Recreation Information Station in Forks. Phone: (360) 374-7566
Staircase Ranger Station near Hoodsport. Phone: (360) 877-5569.
The vast majority of those camping for a Bretherton summit will do so at one of the many campsites at Upper Lena Lake. There are bear wires to hang your food from, which is handy. Upper Lena Lake is a popular backpacking destination so get an early start if you want your pick of campsites.
Upper Lena Lake Camp
Another option is to camp at the often crowded and even more popular Lower Lena Lake, some 4 miles closer to the trailhead. One benefit to the lower lake however, is the opportunity to use it as a base camp to bag the peaks around Upper Lena and The Brothers all in the same trip.