This is a long hike. It is about 13.5 miles round trip. The trail head is at about 5600 feet, and Windy Pass is at about 8900 feet, so the first 6 miles you gain 3300 feet. In the last mile you gain over 1100 feet in .8 miles, so the last part of the trail is pretty strenuous. Watch out for the dang caterpillars, they're everywhere.
From I-15, take exit 275 to highway 52, and continue on to highway 189. Drive up Provo Canyon to Vivian Park and turn right at the South Fork Provo Canyon Road. Continue up this road for about 5 miles and right before it dead ends, park at the Great Western Trail Parking Area.
From the GWT parking area, pass the gate at the west end of the parking lot. Walk up the small dirt road for .8 miles, and before you get to the second gate take a left onto a smaller hiking trail. Follow the signs for The Great Western Trail no. 58, and there is also blue paint on some rocks to help define the trail. The trail is super easy to follow and way obvious, so if in doubt, you probably wondered off of the trail. Follow the trail for another 3.5 miles until a fork in the path. Take the left fork towards Windy Pass. After another 2 miles you are on top of the pass, and turn right and try to take the best route to the top. If you stay on the north side of the aspen trees you can find a faint trail that leads to the top. The further you go the more clear the trail gets.
In summer a good pair of sturdy hiking boots is a must. Also a bunch of water because it gets hot, and it's a long hike. In winter crampons, ice axes, snowshoes or skis, and avalanche gear is necessary.