after you found the geocache Thai–Lao Friendship Bridge Nong Khai you might want to enter the bridge itself.
Leave your vehicle at one of the parking lots, find the entrance gate (at the blue sign there is a complete new entrance left to the sign) and take the left route to enter the bridge. Going to the right is also possible but you might meet some "officials" ;-)
enjoy the great views at the cache location. If you're lucky and are at the cache location at the right time (14:50 is a good time) you might see the train running between "Nong Khai Railway Station" and "Thanaleng" in Laos (video).
When you return to the parking area, have some food and drinks at the local businesses under the bridge...
PLEASE:
if you cross the bridge with any kind of vehicle: under no circumstances stop there and park to search for the cache!
BYOP