Petrified Forest National Park is about 10 miles east of Holbrook. The North Entrance to the park can be reached by taking I-40 north east from Holbrook. The South Entrance can be reached by taking SR 180 south east from Holbrook.
If you plan to continue driving east on I-40 toward Albuquerque after leaving the park, I recommend that you use SR 180 and the South Entrance to the park, to avoid back-tracking back to Holbrook to get on I-40.
There is a park entry fee of $10 per car, unless you bought a $50 pass for unlimited use in all National Parks.
A single road (10-15 miles) goes through the park from SR 180 to I-40, there are several stopping points, overlooks, and a Visitors Center (recommended).
Along the way, there are easy trails that provide views of fossilized wood/trees that have slowly turned to stone over 200 Million years.
Do not remove any of the petrified wood from the park. The National Park Service is very serious about that.
There is a large gift shop that is next to an Information Center with lots a fossils, and even a couple of small dinosaur skeletons.
This is said to be one of the largest concentrations of Petrified Wood in the world.
There are more spectacular National Parks, but as I thought about the 200 million years it took to produce these fossils, I gained appreciation for the park.