Gravel road to a former car-camping site with numerous re-routes/washouts. A few chunky sections that require some mountain bike skills, but very doable on a drop bar bike. There are a handful of waterfalls accessible by short hikes from the trail including Chenuis Falls across the river (if the bridges are in), Ranger Falls one mile uphill, and Ipsut Falls 1/4 mile from the terminus of the bikeable section.
The campsite has bear lockers for food storage and pit toilets. Water should be filtered from nearby tributaries as the Carbon River is too silty! Most sites have options for hammocks, but trees are big here so plan accordingly!
This year, Rainier started issuing Wilderness Permits through Recreation.gov. You'll need to snag one of those, or check the website for available walk-up sites and get in line early at the Carbon River Ranger station. Permits need to be collected by 12PM the day of, or up to one day prior to arrival.