Monarch Grove Butterfly Sanctuary is a must-see for butterfly lovers. Tourists and locals alike flock to the outdoor Sanctuary every winter to see thousands of beautiful Monarch butterflies clustered on pine, eucalyptus, cypress and redwood trees, in Monterey’s Pacific Grove. Monarch butterflies arrive at the Sanctuary in October where they wait out the winter season until late February. The best time to see them is when they are their most active between 12 noon and 3pm on sunny days.