Hosmer Grove Loop Trail is the first hike one can experience inside Haleakalā National Park. If youʻre planning on hiking all day up here, this is also a great warmup hike. Right after entering the park, take the first left turn you see to get to the parking lot and bathrooms. The first thing youʻll notice once you step out of your vehicle is the rich smell of eucalyptus, cedar & pine emanating from the grove nearby. These invasive hardwood tree species were brought in from all over the world by Ralph S. Hosmer in the early 1900s.