Nine miles of hiking per day is not gruelling but it's enough to feel like you did something. I did half-dome in Yosemite many years ago, and if I remember it'

Nine miles of hiking per day is not gruelling but it's enough to feel like you did something. I did half-dome in Yosemite many years ago, and if I remember it's about 7 miles one-way with ~4000-5000 feet of elevation change. But the trail is mostly quite good, and it's as much as I'd want to hike in a day. For a two day trip, especially if the trail is rough, 18 miles sounds about right.