It was raining a little bit when we went. We donned our ponchos before hiking. Our children were with us ages 5 and 6. We did the hike quite easily. It took about 15-20 minutes. As you get close to the viaduct there is a turn off on the left side where another path goes up the hill steeply. This allows you to be almost at the same level as the train for better pictures. Being on the left side of the viaduct is great for the morning train crossing as the train would be coming towards you. In the afternoon, it's probably better to be on the right side of the viaduct since it's the return trip and the train would be coming from the left side. It was great to see the Steam engine bellowing smoke down the tracks. Well worth the pretty hike!
Just fyi, if you go past the visitor's center there is free parking just after the bridge. It is also the start of the trail to go towards the viaduct. Also, we were in position by 10:35am to wait for the train to come through. Don't be late or you'll miss it!