Easy Trail

Mount Bailey near Diamond Lake is a great hike to fantastic views but it requires some effort to get those views - with a hike of about 10 miles round trip 

There's enough room to pull a vehicle off to the side by the gate on Heimer road.  This is an easy trek with a very gradual elevation change.  The trail is a nice groomed gravel road that leads all the way to the summit. 

 If you keep veering right at all the forks in the road, evenutally you will end up at the summit on a nice wide gravel plot perfect for setting up a decent station.  Not a whole lot of shade to be had here, unless you climb off the path.

Here's another summit in the Diamond Lake area to activate if you have a few hours. It's a drive-up, if your vehicle has moderate ground clearance and otherwise a short road hike. 

Buck Mountain is a summit with a short hike of less than half a mile that you'll want to do along with Coffin Mountain (W7O/WV-005) and Bachelor Mountain (W7O/WV-003).

Take Highway 22 east 19 miles past Detroit, Oregon and turn right onto paved FS 11.

Bates Point (Peak 2360) is a drive-up summit in the Coast Range of Oregon - specifically in the Tillamook State Forest. Roads in the Tillamook Forest are usually good - however the signage and documentation are remarkably poor. What's on the ground doesn't necessarily match your GPS map or what in Google Earth and vice versa.

Access Info:  Take SR25 south from Randle or north from Cougar.  Head west on SR99 for 4.5 mi to the Bear Meadow Viewpoint.  Restrooms at the viewpoint parking area.  Read the interpretive signage at this viewpoint since this is where many of the iconic photographs were made of the St. Helens eruption in process by photographer Reynolds, who barely escaped with his family.

Just north of Detroit, Oregon are a nice bunch of summits - Dome Rock is especially good. The Tumble Ridge Trail takes you to Dome Rock on a pleasant forest hike of only about 1.5 miles and 500 feet total gain.

There are several ways to get to Green Point Mountain - I choose the shortest hike, which of course required the most uncomfortable drive (i.e., high clearance and paint you don't care about).

Tanner Butte is perhaps the most remote SOTA summit in Oregon's Northern Cascades. Despite many resources that point out the trail length at 17 miles, measured from the GPS track it shows up as right at 20 miles round trip, with 4500 feet of elevation gain. You won't see many other hikers on these remote trails.

I echo AK5SD's comments.  Don't go thru the gate but park in nearby areas at the gate.  This road is frequented by fire crews and other Rangers who may be only visiting the lookout for a few minutes.  Don't get caught behind a locked gate!   And the lookout road is mostly a one-way which would create problems if you met traffic.  It's only about a mile hike (750 ft elev gain) from the gate to the lookout.