The Quill is a dormant stratovolcano located on the island of St. Eustatius in the Caribbean Netherlands. It is the most prominent geographical feature of the island, rising to an elevation of approximately 600 meters above sea level. The volcano's name is derived from the Dutch word "kuil," meaning pit or hole, a reference to its distinct crater.

The volcano's last known eruptive activity occurred in the Holocene epoch, with its most recent eruptions estimated to have taken place around 1,600 years ago. It is classified as a potentially active volcano, though it has been in a state of dormancy for centuries. The structure is characterized by a large, forest-filled crater, which is the result of a prehistoric collapse of the volcanic cone.

The crater of The Quill forms a unique and biodiverse ecosystem, officially protected as The Quill National Park. The park encompasses the entire volcano and its slopes, covering an area of several square kilometers. This protected status helps conserve the rich variety of flora and fauna found within the crater's interior and on the outer slopes.

Within the crater, the environment transitions through several distinct ecological zones due to variations in elevation and moisture. The crater floor supports a lush rainforest, home to numerous tropical plant species, including elephant ears, ferns, and fruit trees. This enclosed environment creates a habitat for various bird species, hermit crabs, and other wildlife.

The Quill is a popular destination for hiking and ecological tourism. A well-maintained trail system allows visitors to ascend to the crater rim and descend into the crater itself. The hike to the summit offers panoramic views of St. Eustatius and the surrounding Caribbean Sea, while the descent into the crater provides an immersive experience in a unique tropical forest environment.

From a geological perspective, The Quill is part of the inner volcanic arc of the Lesser Antilles, formed by the subduction of the Atlantic Plate beneath the Caribbean Plate. Its composition is primarily andesitic and dacitic, which is typical for stratovolcanoes in this region. The volcano's formation and activity have significantly shaped the topography and soil composition of St. Eustatius.