The beginning of the trail is challenging and steep, but the grade mellows out after about 0.5 miles. Once you settle into a rhythm, you can appreciate the beautiful trees that give you shade and shelter from the wind.
There are a couple of intersections, but like the rest of the South Park system, directions are clearly marked.
Near the top of the trail, you'll cross the Monument Peak Trail
where you might be tempted to go left, but if you continue straight on the Flume Trail, you'll get to the top of Monument Peak, and then be able to come down on the trail you crossed.
The last bit of the Flume Trail gets very steep (might be a hike-a-bike section for some) but it is short, and you are rewarded with views of Spanish Peak and the rest of the northern Sierra.