Nature
It may seem silly, but some two-year-olds think a walk around the block is as exciting as a trek through the jungle. Being outside is not only interesting for a child, it is good for her. It gets her off the couch and out in the fresh air, gives her time to learn about the world, and is also beneficial for her mood and health.
Lots of stores sell bug collectors, which typically are wooden boxes with wire (so the bug can breathe and your child can see it). Though this is something you can easily make with your child, you could simply go on a bug hunt with a magnifying glass and a net. Your child can look at the bug, but you don't actually have to bring it home. Explain that the bug needs to be left alone in order to live, but like scientists, the two of you can examine the bug closely.
Taking along a basket or grocery bag, go for a walk through the woods with your toddler. Have her pick up anything she wants (rocks, leaves, sticks). Promise that you will keep everything for a day or two so that she can look at what she collected when she's home. Leaf rubbings (made by placing a leaf under a piece of thin paper and rubbing over the paper with a crayon) are a little difficult for a two-year-old to do alone, but you can have her glue some of the smaller findings to construction paper.
Getting your two-year-old a children's gardening set is a good investment — she will be able to rake, shovel, and dig near you in the garden without getting hurt (since such tools will be child-sized and made of plastic). If you don't encourage your child to dig along with you, she's unlikely to let you garden in peace. Give her some seeds (sunflower seeds are good) to put in the holes you dig together so that later she can watch them grow.
