I've actually been here: http://mrgris.com/travel/blog/labrador/2/ Quite a weird place, though definitely not 50m tall.
From a bit later in the trip is a photo from the shore of Manicouagan Reservoir. According to Wikipedia [1], it's an annular lake formed about 214 million years ago by the impact of a meteor 5 km in diameter. It has an outer diameter of about 72 km, and it's "the Earth's sixth-largest confirmed impact crater according to rim-to-rim diameter", and one of the oldest known. [1] https://en.wikipedia.org/wiki/Manicouagan_…
One of my favorites is lake mistassini[1], an immense lake shaped like claw marks