The walk starts at a signposted car park at the western end of Loch Achray. The car park is right on the north shore of the loch, on the A821 from Callander or over the Duke's Pass from Aberfoyle.
Cross the A821 and join the signposted trail. The path winds through woodlands before joining a stream. The going is easy, and the woodlands are open. If the weather has been wet there can be areas of mud, so good waterproof footwear is advisable.
The path now gets quite steep, but even then the going is not that difficult, as stone steps have been created on the path in a pretty successful attempt to counteract erosion. You can't go very fast through this final stretch to the top, but it is not terribly difficult. Our 5 year old daughter made it, and was pretty cheerful about it, though she did have to be carried when the path crossed over a mountain stream.
At long last the path emerges at a shoulder of land just under the true peak. A short stroll to the western edge of this ridge reveals Loch Katrine spread out far below. If you are lucky you can see the steamship SS Sir Walter Scott as it carries passengers up the loch.
If you fancy a final scramble it is only the matter of a minute to reach the true summit. The view is magnificent, but it can also be windy, so be prepared for a buffet!
The weather can change very, very, suddenly. I lost track of the number of times I put my camera away, thinking, "There's no point trying to photograph in this", only to take it out again two minutes later.
A reasonably fit person should reach the top in 1-1/2 hours. The entire walk took our family of 4, including children aged 12 and 5, about 3 hours up and down with plenty of stops for rest and refueling - and an extended stop huddled behind the inadequate shelter of a boulder near the summit when the weather turned suddenly foul.