Actually there is access for the lower end at MP 58.3 on Highway 2, nice parking area and an honest to Hoyle Caboose.
The trail has a fork in it, righteous one goes up and up and catches the RR bed near one of tunnels, most are in some state of collapse (like many of us) and yer not supposed to go in.
Rules...
Here's one now
Since its an old RR bed, the walking is very easy, great in Spring and Fall.
A chunk follows a huge wall for a long distance, long enough to appreciate the tough buggers that blasted and built with liquid rock.
With Cougar, Bobcat, Bear and the crazed deer you kinda feel it would be easy for some such critter to watch you wander by from the top.
Most the old trestles are long gone, replaced with foot bridges you could drive a fine German auto over.
Or hang off of.
Quite a good book out there about it... well researched and written to keep your interest with eye witness accounts, it follows the timeline of events and decisions leading up to the disaster as well as the efforts afterward to save survivors and recover the victims:
The White Cascade by Gary Krist.
No affiliation I tell ya.
Quite a slice of history and only about 90 minutes from where I live.
There are some crazy cool stuff here in the PNW within 5 hours drive time... desert, rain forest, mountains, lakes, rivers, the ocean, the Salish Sea...
Tough part for me at times is just figuring out what to go do next.