Hands down one of my favorite spots to bring visiting friends and family to "hike". The Hoover dam in one of my favorite places in the country, and this trail bleeds history. 5 tunnels in total, tunnel number 3 half way in, take a flashlight and shine it upwards (but please only for a brief second) and you can see the hundreds of bats that live in the tunnel. Hence the "pee" smell.
If you follow the trail past the 5th tunnel, it will continue to take you to the top floor of the parking garage of the dam. If you continue this path there is a fork. One is labeled "easy" and a shorter trek. Please don't skip out on the longer trail as you will stumble upon the Hoover dam grave yard. This is where they store the old retired parts of the dam. It gives you a better perspective of just how big the pieces inside the dam are. And also proves the truck commercial where they tow a turbine out of the dam with a pickup is false.