Museums offer a plethora of interesting and notable objects. I happen to live in New York City and have access to some world class museums. I often spend my leisure time perusing collections of art and artifacts while snapping as many pictures as possible. Sometimes even the architecture of the museum itself is inspiring enough to photograph.
Museum photography can be difficult, as the lighting is sometimes dim and a high ISO is required. However some museums, such as the Metropolitan Museum of Art, offer permits for tripods on designated days.
One important thing to note however, is that while many museums allow photography, few permit the sale of those photos for commercial purposes. It's important to upload these types of photos as editorials.
If you want to discover an array of interesting subjects you can't find elsewhere, check out your local museum. You're sure to diversify your portfolio!