This was the first drain I explored and it's choice was mostly down to its convenience and lack of possible onlookers. There wasn't anything particularly interesting inside, but that didn't matter, it was a first and an experience to remember.
"Twenty years from now you will be more disappointed by the things that you didn’t do than by the ones you did do. So throw off the bowlines. Sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover" Mark Twain