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FATMAP difficulty grade
The Aiea Loop Trail is a popular 4.8-mile Oahu hike.
Along this gorgeous hike, you'll enjoy views of the southern coastline of Oahu, Pearl Harbor, Diamond Head, nearby mountain ranges, and an impressive stretch of elevated interstate running through the rugged mountains. The trail itself can be very rugged in places, traversing slick root webs, mud, and some rocks.
However, this loop isn't too steep or strenuous in the grand scheme of Oahu trails.
According to FATMAP, it gains a bit over 1,000 vertical feet over the entire loop. Sources: https://dlnr.hawaii.gov/dsp/hiking/oahu/aiea-loop-trail/