The pedestrian walkway runs from Riverfront Park to Sacajawea Park and includes a fishing pier that extends out into Flahead Lake under the Armed Services Bridge. Parking is available at both city parks and the cache is a short walk.
The parks are very popular during the summer months as they offer great views, grassy slopes, playground, fishing, swimming and a boat launch. Muggles are always around so SUPER STEALTH is required. Better to score this one with a group of people to provide cover as you make the find. Alternatively early morning or evening work well.
You are looking for a small cache tucked out of sight with room for just a logbook. You can reach it from the cement path, no need to climb outside the railing. 
Fisherman's Wharf