The Niagara Glen is managed by Niagara Parks who provide facilities, access, and maintainance. The glen hosts a wide variety of things to do including picnicing, hiking, fishing, birding, and of course, bouldering. Bouldering access is a cooperative effort between Niagara Parks and the Ontario Alliance of Climbers.
Bouldering
Each person who wants to climb at Niagara glen will need to fill out a waiver and acquire a permit. Permits may be purchased either in person or online, for either single day or annually, and includes a complimentary parking pass valid at the Niagara Glen for up to two registered vehicles (though I think only one at a time) for as long as the permit is valid.
In-person permit purchases may be done at the Niagara Glen Nature Centre which is open seasonally from April through November or at the Butterfly Conservatory located less than 1km down the road from the Niagara Glen and open year-round. Online purchases may be done through the bouldering activity page on the niagara parks website; however, the online purchase only provides a receipt which must be redeemed for the actual permit and parking pass at the nature centre or butterfly conservatory. The online purchase receipt may act as a temporary permit but I have not been able to verify this so do so at your own risk.
Be sure to familiarize yourself with the bouldering rules before heading out to climb. The official bouldering rules don't mention it but rope climbing of any kind is strictly prohibited, this includes but is not limited to: top rope, trad, and any sort of aid for bouldering.
Trails
The glen can be a confusing place to nagivate for the uninitiated so it would be wise to bring either a trail map, or better for us boulderers, the Niagara Glen Bouldering guidebook.
Avoid the use of unsactioned spider trails. Many of the boulders lay off the main trails and the guidebook will show the side-trails that should be used to access these boulders. Do not attempt to blaze your own trail; Niagara Parks has on several ocassions expressed concern about the use of unsanctioned spider trails which damage the plant life and jeopardize access to climbing at the glen, not to mention you may end up in a closed area or wading through a big patch of poison ivy.
Closed Areas
There are various areas of the glen that are closed; usually for reasons of safety but may also be for maintenance, overuse, or otherwise. Niagara Parks will have the most up-to-date info on any closures and usually provide signage for closed trails, however, signage may not always be in place so don't assume an area is fair game just because there is no sign indicating otherwise.
Most of the areas nearest the river (Bizarro river and Oz river in the guidebook) are now no-trespassing areas, as such the boulders within them are closed. Being in these areas will result in fines. The whirlpool trail and by extension the whirlpool boulders are also often closed for safety reasons due to water levels.
Parking
Paid parking is available year-round at both the glen and the butterfly conservatory; however, the parking lot at the glen tends to fill up in-season when the weather is nice. Times will vary but it's relatively common to see the parking lot full by 11am and remain full until late afternoon on nice weekends.
Fret not when the glen parking lot is full as there are still some options: Do a few laps around the parking lot — there are people regularly coming and going from the glen so you may get lucky and snag a spot. Or, park down at the butterfly conservatory — there's often parking available there and the hike over to the glen is less than 1km.