I cannot recommend this trip/tour enough. I just happened to be in St. John's for a wedding and decided to stay an extra day just to do this. Mistaken Point is a two-hour drive from St. John's followed by a relatively easy one-hour hike along the Atlantic coast.
The fossils themselves are imprinted on horizontal rock sheets (don't know the technical term) that stick out over the ocean. You can literally walk on the imprints, which is why you have to take off your shoes first. I'm not kidding when I say there are HUNDREDS of fossils dotted all over the sheets.
The fossils are obviously amazing, but the hike is beautiful as well. Crashing waves, the open ocean, and wild blueberry bushes lining the trail.
Oh, and the whole thing was only 23 CAD per person! Seriously, if you're ever in the area, don't skip this.