Snoqualmie Railroad Trestle is a very photogenic spot and part of local culture and history
The best way to get the old railroad trestle is by using the Preston-Snoqualmie trail. There is a parking lot for the trail located just across from SE 56th Place, Fall City, Washington, 98024. After parking, hop on your bike and pedal east on the Preston-Snoqualmie trail for about 2 miles.
The trail is mostly flat and paved, so you can get away with using your road bike. Eventually, you will reach a fence where the trail ends, to get to the railroad trestle you will need to walk around the fence (which is not hard at all). After getting around the fence, continue on the dirt path for another 150 yards until you reach the end where the trestle begins.
It's possible to get out on the railroad trestle itself and go down to the side of it as well. Exercise extreme caution if you venture out onto the trestle. It is approximately 200 feet tall and you'll have to carefully crawl out on the 9 inch beams to get out to the middle of it. You will also notice that it is possible to hear Snoqualmie Falls from the trestle. Have fun and be careful!