I'm in complete agreement w/many here, the 'floating' buildings and Cinesphere must stay.
I also quite like a lot of mature trees on the site.
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That said, there is something amiss w/the place, as revealed by the fact I was last there to see the original Lilith Fair....10 years ago?
I would break down the issue with Ontario Place this way.
1) Connections, it does have some good stuff now, though not enough.......but what is there just feels so isolated from the City, in many ways more so that the Toronto Islands
Resolving this is not that easy, of course, as the isolation occurs from
a) The Gardiner
b) Lakeshore
c) The Ex ( a barrier in that during the off-season the Ex feels like quasi-private and often under-used space
d) The Railway
e) OP's own parking
That's a lot to overcome
In the short-term, I see very little to be done about the Gardiner, except giving the underside a nice paint job and under-lighting.
The railway is what it is; and I wouldn't want it removed......Lakeshore could re-routed north....but not easily..........what could be done......would be to change the area grades; as right now Lakeshore is almost in a valley/gulley btw the Ex and OP. If the edge of the Ex/OP were lowered, and Lakeshore raised a bit, so it felt more like an urban boulevard w/sidewalks etc. that might help.
The parking as it stands, must go.......some reduction, some underground, if feasible, and possibly a 2-level parkade for part of it, to reduce the footprint by as much as 75% so that OP could meet Lakeshore in a welcoming way.
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2) OP as a passive place, park, a few shops a place to paddleboat/canoe etc. This is part of its charm (though by no means all of it); but this part needs some touch-ups............at least one, ideally 3-5 restaurants worth eating at, with outdoor, water-facing patios......it could be quite the destination, particularly in summer. Either existing low-use islands, or a new one could showcase nature, a coastal-lakefront forest/meadow and...
And how about a beach.............a real honest to goodness, beach for downtown........
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3) The active stuff...........for the little ones, can we have the Original Children's Village back? And the caboose that served the really great fries.....(childhood memory)
More than that......how about a top-notch water park (double the current size, better than Splash works etc.
Finally, keep Cinesphere, but bring back its futuristic vision........start by refitting the theater with those new-fangled movie seats Cineplex is testing that move with the movie......
Then change the lighting on the building (and adjacent buildings) to mimic the CN Tower in putting on multi-coloured fantastic light show each night.
3b) At the Ex site, but operated for the full OP Season, bring back one truly awesome Wooden Roller Coaster......THE NEW FLYER....lit-up at night with LED on every wooden beam in all sorts of fantastic colours and a light show that moves with an in-motion coaster.
There....think I've covered it!