Tiger Mountain is in about the middle of the Tiger Mountain State Forest southeast of Issaquah. Access is via a gravel forest road and you may want to use a GPS or track your mileage as any signs may not lead you clearly to the summit. You'll need a Washington State Discover Pass for this location.
Find the West Tiger Mountain Parking Lot off of Highway 18 (near 47.466° -121.931°). You can park right in this lot or the upper lot if the left gate is open, but the distance and elevation gain are not much different. Take the right gate and head up the forest road about 2.6 miles. At the junction go right for about 0.5 mile, and then left about 0.8 miles to the summit.
These roads are used by mountain bikers and that would be a nice way to activate this summit - the ride down would be easier than walking on the road. The summit had a picnic table in 2012 and a small repeater site - no RFI was noticed in an HF activation. There are a few trees to string antennas from, but have a care to not string wire across or near the road as cyclists do make it to the top and may not keep exactly to the gravel roadway.
You might consider doing both West Tiger Mountain and Tiger Mountain as you'll be covering the same 2.6 miles (one way) on the main road to access either summit. See www.pnwsota.org/blog/k7atn/2012-july-30/west-tiger-mountain-wa-july-2012.