Montessory Pedagogy is all about exploring and sensorial learning. This one is a great option as you can go to any park with your toddler, pick the best nature themed objects and bring them back home to your Nature Treasure Box. You can even make it a seasonal activity by changing the box with the arrival of a new season (the Spring Box, the Christmas Box, etc)
Remember activities with Toddlers only last for a few minutes so make sure to change it up from time to time, add or remove objects, and always revisit every day or so!
Safety First! Always make sure to pick appropriate sized objects, avoid any sharp or pointy items and check before bringing any uninvited guests home (i.e. termites, bugs, etc).