Mare Crisium, or the Sea of Crisis, is an exceptional formation. It is actually a lunar basin, a large area of that was flooded by the impact of an asteroid billions of years ago. The flooded lava floor is oval in shape. The east-west direction is 375 miles; the north-south direction is 345 miles. This is the only major mare that is not connected to the great mare system on the earth facing side of the Moon. The floor is surrounded by walls of mountain massifs many thousands of feet high. They rise abruptly from the dark floor. There are many wrinkle ridges, small hills and flooded craters scattered around the sea, concentrating mainly around the edge. At any star party or public observation this is a must formation to show.
Picard (14 miles wide) is a nice crater out in the Crisium Mare. It is over a mile deep and easy to see in a 2.4 inch telescope.