Straddling the border of Poland and Belarus, Białowieża Forest is the last remaining old-growth forest of Europe. The forest covers nearly 1,200 square miles, a massive ecosystem that has remained, for the most part, unspoiled by humans for the past 7,000 years. It is home to a vast array of flora and fauna, including the European bison, the biggest land mammal in Europe.

Recognized as a UNESCO World Heritage Site, the Sundarbans Reserve Forest in southwest Bangladesh is the largest contiguous mangrove forest in the world. Mangroves are trees and shrubs that grow in low-oxygen soil along slow-moving coastal waters. Covering 3,900 square miles, the Sundarbans Mangrove Forest borders the Bay of Bengal and the river delta formed by the Megha, Ganges, and Brahmaputra rivers.

Even though it’s only 11,000 acres, the Tuskegee National Forest in eastern Alabama has plenty of opportunities for enjoying the outdoors. One highlight is the eight-mile-long Bartram National Recreation Trail, named for naturalist and writer William Bartram, who traveled through the area in the 1770s. While there is a tiny 33-tree “forest” in Adak, Alaska, that calls itself the country’s smallest national forest, it’s not actually part of the National Forest System.

Stretching nearly 250 miles along the north and central coast of British Columbia, the Great Bear Rainforest encompasses about 21 million acres. It’s one of the largest remaining coastal temperate rainforests in the world, sometimes referred to as “the Amazon of the North.” Its name comes from the Kermode bear, or spirit bear, a very rare subspecies of the black bear found only in this rainforest.

Petrified Forest National Park, located in the Apache and Navajo counties, contains swaths of petrified wood deposits across a shrub-steppe semi-desert badlands. The 225 million-year-old fossilized fallen trees were once part of an ancient conifer forest. It was made a national monument in 1906 and has been a national park since 1962.

You might want to bring some breadcrumbs with you if you're trying to find your way across Sweden, the most forested country in Europe with 28 million hectares of forest. The next most forested countries in Europe are Finland, Spain, and France. Sweden and Finland have some of the strongest protections against deforestation on the continent, with tree coverage at nearly 70% of each country’s surface area.

The Danish territory of Greenland is one of only four countries or territories without any forest area, along with Qatar, Nauru, and San Marino. Wondering what technically qualifies as a “forest”? That includes natural or planted tree systems with trees that are at least 5 meters (16 feet) tall — and trees in gardens, urban park areas, or agricultural production systems don’t qualify.

In 2013, scientists announced that an unnamed Great Basin Bristlecone Pine, located in Inyo National Forest near Yosemite National Park, had been verified as 5,062 years old. Other trees on Earth are reportedly older than these two in California, but they are colony trees that clone and reproduce — in other words, large groups of trees that are connected by a single root system.

Cloud forests are similar to rainforests, but are located in mountainous regions and have areas of high elevation roughly 3,000 to 8,000 feet above sea level. First established in 1972, the Monteverde Cloud Forest Reserve stretches across a vast 35,000 acres in Costa Rica. The damp air and lack of sunshine slow down the rate of moisture evaporation, which results in incredible biodiversity.

Rising in the Black Forest Mountains of Germany and traveling through nine countries — Ukraine, Romania, Bulgaria, Serbia, Croatia, Hungary, Slovakia, Austria, and Germany — the Danube collects water from more than 300 tributaries along the way and empties into the Black Sea. The 1,700-mile Danube flows through more national capitals than any other river, including Belgrade, Vienna, Bratislava, and Budapest.

It was only in 2009 that scientists uncovered the remnants of an ancient root system just outside Cairo, New York, that hadn't changed much over the course of 385 million years. The fossilized roots are believed to be part of Archaeopteris, a genus that yielded the first modern tree. Reaching out around 18 feet from their trunks’ bases, the tree roots once dominated forests around the world.

The world's largest rainforest is located in South America, but the largest forested area on Earth starts in Eastern Europe and stretches all the way to Siberia. Comprising 808.8 million hectares, these boreal forests make up over 25% of the Earth's forests. Though they don’t include a wide diversity of tree types, the forests play an important role in keeping carbon out of the atmosphere.

In a quiet northwestern corner of Poland is a groove of around 400 pine trees whose bizarre shapes have long baffled scientists. The majority of the trees of the Crooked Forest possess a 90-degree bend at their base that points due north. Some say that it’s due to a gravitational pull in the area, while others suggest that heavy snowfall flattened the trees when they were young.

Though the Amazon covers 1.2 billion acres, the world’s second-largest rainforest is nothing to sneeze at. The Congo Rainforest stretches over 500 million acres — bigger than the entire state of Alaska. It is home to 10,000 species of tropical plants (30% of which can be found nowhere else on Earth), 400 species of mammals, 1,000 species of birds, and 700 species of fish.

There's more to the Northeast than just cities — especially if you head all the way up the coast to Maine, a largely rural state that is 89% forest land. Neighboring New Hampshire takes second place (and actually finishes ahead of Maine in tree cover, which is a little different — a tree on a golf course, for example, counts as tree cover but not forest land).

At about 52,500 cubic feet when it was last measured accurately in the 1980s, General Sherman is the world's largest tree by volume. (For reference, that's about half the volume of an Olympic-size swimming pool.) But despite being big, General Sherman is not particularly old by sequoia standards — the tree is only about 2,000 years young, whereas other sequoias are thought to be more than 3,000 years old.

Tongass National Forest in southeast Alaska covers 16.5 million acres, which is roughly half the size of North Carolina. There’s no shortage of activities for visitors, either. Take a hike, spot some eagles, camp, fish, or ride a dog sled across a glacier. There are also several cultural centers in the forest, where you can learn about native culture, geology, and wildlife.

Missouri’s only national forest is named for one of the most famous Missourians. Mark Twain National Forest covers approximately 1.5 million acres of land in and around the Ozark Mountains, in the central and southern parts of the state. But while the park is home to a number of notable springs, caverns, and volcanic mountains, it was never home to Mark Twain.

The Black Forest covers a large mountainous region in the state of Baden-Wurttemberg in southwestern Germany. It's home to several picturesque towns and villages, including Baden-Baden, renowned for its spas and thermal baths, and Triberg, which boasts one of the world's biggest cuckoo clocks. The Black Forest is also known for its hiking, skiing, and jewelry production.

The Amazon is the largest rainforest on the planet, touching nine countries: Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Peru, Suriname, and Venezuela. It covers more than 2.1 million square miles (approximately 40% of the South American continent) which is about the same amount of space as the lower 48 United States. More than 60% of the Amazon falls within Brazil’s borders.