This was about three years ago. There was this intern in one of the offices I was taking care of. I was a janitor at the time. She was about 5'6", nice hourglass shape, curves in all the right places, long brown hair, sparkling blue eyes, and a nice set of breasts; a handful, but not too big. We had been flirting a bit over several weeks, innocent stuff mostly. I don't remember exactly how it happened, but we were in the hallway and got on the subject of a set of tunnels, linking several buildings in the complex. I had been through them before. She hadn't. I jokingly offered her a tour some night after she had finished work. Two nights later she took me up on it...
So we waited until roughly 6pm when most people have left for the night. She's dressed in a skirt, button down blouse, heels and stockings, and wearing glasses (I have a thing for glasses). So I open the door to the stairs which lead to a little maintenance shop. I go first to make sure there's no one there then motion for her to follow. We walk over to another set of stairs which lead into the tunnel system. Being the gentleman, I help her down the stairs as they are cracked and worn, and lead her through the first tunnel which is narrow and has a little ditch for the rain. I lifted her at one point to cross over an intersecting ditch and cracked floor, feeling her arms around me, her breasts against my chest, being separated only by the clothes we were wearing. As I set her down, she kissed my cheek and thanked me. Made me blush a bit and she commented about how cute I looked, which made me blush even more. We walked further, our only light coming from small light sockets placed about every 20 feet apart. We came up to a crossroads. Four tunnels, three different directions we could go.
We had just come from the tunnel leading east, so I explain where the north and west tunnels lead. The tunnel to the south was partially blocked off as the company does not own that particular building. But there are still conduits and lights leading that way, so there was enough room at the top to get through if needed. There was also a ledge about two feet high so you could lift yourself over. She looked down each tunnel as I explained them, then walked over to the blocked off one, asked me to help her up so she could get a better look. I held her hand as she stepped up, then she placed my hand on her hip to steady her. I placed my other hand, standing right behind her, looking at her ass, on her other hip. She looked down the passageway for a minute or so, then placed her hands on mine, I assumed to step down. She took my hands and moved them slowly to her breasts. This drew me into her, and my head against her back and her ass against my chest. She looked back at me with a grin on her face to see a bit of a shocked expression on mine. She told me she was moving on in the company soon and wanted to thank me. I have never gotten so hard so fast. She asked me to help her turn around so she could look at me. I did, and she was smiling this seductive little smirk.