You have two choices. Hop the MK bus, and then take the boat to Fort Wilderness.
OR
Head over to the Studios, and hop the Fort Wilderness bus, which drops off near the Hoop.
Reverse the process to get back. If both parks are closed, you'll need to take any bus marked OUTPOST. From there, transfer to the Downtown Disney bus, and then transfer to the Fort Wilderness bus.
If you have a car, it's simple to get to Fort Wilderness. Exit out of the Dolphin by taking a LEFT. Then take a RIGHT onto Buena Vista Drive, and an immediate RIGHT onto World Drive. After you go through the toll plaza, stay to your far right, and keep going right.
You'll want to go to the SECOND entrance to Fort Wilderness (there will be signs for Pioneer Hall). From there, you'll want to take any bus that says SETTLEMENT. Color does not matter.
To get back to your car, board any bus marked OUTPOST. When you leave the parking lot, take a LEFT onto Vista Blvd. At the traffic light, take a RIGHT. Follow that down to Buena Vista Drive, and take a RIGHT. You'll come right up to the Epcot Resort area.
