The simplest means of getting to Sentinel Dome is taking the canoe route mentioned in the getting there section where you start at the main campgrounds on George Lake into Freeland Lake, take the half a kilometer portage to Killarney Lake and then paddle Killarney Lake over to OSA Lake where I would suggest taking the longer of the 2 portages as it is the most direct path and is actually the path of least resistance as well... despite how the numbers may read.
Look for the natural opening on the Northeast corner of the lake right where OSA Lake narrows. On the left is a little rock fall and you can beach the canoe on a series of ledges just to the right. The opening is natural and is readily recognisable even at a distance. Once you make your way into the woods, immediately head up the hill to the first rock field... cross this heading slightly northwest. You should be able to make out the next band of rock through the trees in the same direction… follow up this band of rock until it dips down 50 meters or so into a valley with steep rock walls on either side.
In the spring time there is a beautiful waterfall that plunges 20 meters over the rock down to the base where it tumbles down towards Killarney Lake over smoothened pebbles. Stay on the northern side of this stream (side closest to the mountain) and make you way westwards along the northern edge of the valley... you will pass one rockfall... the second rockfall is a 60m high section, keep to the left and negotiate this boulder field.
From the top of this section keep heading straight up the rock bands until you notice a large black outcropping which stands out amidst the snowy quartzite. Head northwest from there until you come up to the face of the Western Wall.
This is the crux of the climb the first section requires some class III scrambling alongside a steep crevasse (around 15 meters deep). From there you can head up to the right which is class three or embark on a fun 15m section of free climbing that is probably no more than 5.4 or so, but is a tonne of fun nonetheless. The handholds are small but firm and the rock is good. At the top you'll have to palm the ridge as it is slightly rounded... but its a straightforward move.
From here the route is class IV for the next 60 vertical meters or so... it requires some route finding, but as long as one is smart and cautious its straightforward. Try and stay on a northeasterly tack here. At the top cross the rock fields northeast, there is one more small class III section and then a quick scamper to the main summit cairn.
Rain gear and warm clothes as the weather is notoriously unreliable here in Central Ontario, a chalk bag, sun screen, lots of drinking water, a walking stick or poles and sturdy boots is all you'd need for the most part... if climbing in summer be sure to bring sun screen and to re apply it as both the rock and water reflect the sunlight and it is very easy to burn.
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