Getting to paradise is not easy.
Lake O'Hara is located in Yoho National Park in British Columbia, Canada, about 10 miles west of Lake Louise (120 miles west of Calgary) and the parking lot for the trailhead and the bus is literally 20 feet off the trans Canada highway. It is well marked.
There are 2 ways to get to Lake O'Hara from the parking lot: bus or foot. By foot, there is an 8 mile trail to the lake from the lot, and you're welcome to hike in, but unless you have reservations at the lodge, campground, or one of the huts, you'll be turned right around when you get there.
The alternate (and quicker) way is to book a seat on a school bus that takes visitors in a few times a day. If you have reservations at the lodge, campground, or hut, you will automatically be secured reservations on the bus. It is $12CAD (about $7US) each way. The ride takes about 30 minutes and is somewhat hair-raising. (I didn't know school buses could climb roads that steep!)
Unless you're staying at the lodge, Ground Zero for you will be Le Relais, the day shelter on the main road just before the lodge. This is where the trail to the Elizabeth Parker Hut is located. Le Relais serves snacks all day (UNBELIEVABLE pumpkin bread and hot coffee) and provides books, maps, and a wealth of information about the area. At night, people squeeze into this tiny hut to hear lectures or stories from naturalists or old-timers.
Lake O'Hara is located in prime wildlife corridor, which means you're GONNA see grizzlies, you're GONNA see elk, you're GONNA see marmots and you're GONNA see pikas whether you want to or not. Be smart. You are in bear country. If you're not used to that, ask at Le Relais for a pamphlet or talk to a park ranger there.
Be smart while hiking. Most of the best trails here are steep, and many are considered "alpine routes" which is a few steps above "trail" so be careful and don't overextend yourself.
Most of all, just sit back and drink in the views of a place that EVERY VISITOR will tell you is the most breathtaking scenery in all the world.
This is no exaggeration!