If you are a birder or if you simply wish to understand a bit more what your senses encounter outside, you may enjoy Learn Bird Songs. As the title says, the site teaches you to recognize the peculiar sounds of various American song birds.
Often, we tune out much of the stimuli around us, including bird songs. We may notice the sound of birds, but we do not differentiate among the multitude of their songs. If you start to pay attention to the songs, you will learn to hear patterns that identify the little performer. This is very useful for noticing species that rarely descend from the tree canopies.
So, open your eyes and your ears, and enjoy the rich diversity of life available for your enjoyment just beyond your door.