More than 400 national parks adorn the U.S., and for limited days this 2017, visitors can visit these parks for free. According to the website of National Park Service, they are celebrating their 100th anniversary this year, thus their free treat to visitors nationwide. They have listed the specific dates on when to access these national parks for free.

This month, they are celebrating the National Park Week, therefore there would be another free national parks' admission on April 15-16 and 22-23. Make sure to not miss out on this awesome offer and visit some of the most beautiful national parks the US has. Here are some parks you should not miss:

Lassen Volcanic National Park, Mineral, California. You might think you're in Yellowstone because of the hissing mudpots scattered all across the park, but you're actually in Lassen Volcanic National Park. Not only is it fascinating for geologists, but visitors will also have a great time exploring the volcanic landscape of the place. The park has all the four major types of volcanoes—shield, plug, cinder cone, and composite, according to Eco Philes.

Virgin Islands National Park, St. John, Virgin Islands. Surround yourself with the clear, blue waters and the serene atmosphere of Virgin Islands National Park. Snorkeling is one of the top activities here, as well as hiking the trails for some of the most magnificent views of your life. The park also has abundant coves and bays that you can wade in in search of luminescent-green parrot fish, leatherback sea turtles, and elkhorn and staghorn corals.

Yellowstone National Park, Wyoming. It's one of the best and most famous national parks in the US and with good reason. You can never be short of adventures here a Yellowstone. Of course, catching an Old Faithful Geyser eruption is something you shouldn't miss, but make sure to embark on some other activities as well. Make sure to also stop by Observation Point, a great part of the park that offers spectacular views of the Upper Geyser Basin.