Rather spooky

Today was a beautiful but very cold day in Colorado. Lawyer Eric met me at the house for a single speed ride around Longmont. We decided to ride east and on the way out of town passed the old sugar beet mill. This mill was once the biggest employer in Longmont, it was built in 1910.The mill closed down in the late 70's and has been abandoned ever since. It has a huge smoke stack and is very visible from all over Boulder County. I've always wanted to check it out. Since we were on bikes, we decided to explore it - rather inconspicuously.
Although, there were fences, it was pretty much wide open. From all the vandalism, you could tell it has been highly visited. But we were very alone today....or so I thought.
There were tons of cool things to check out - dials, furnaces, old office furniture - and many levels.
Eric ascends to a higher level of the mill. There were broken steps and holes in the floor. You had to be quite cautious where you were stepping.
At one point, over 300 people worked here. In this locker, we didn't find any old lunch buckets.
So here's the spooky part:
There was no dust, snow, wind, or smoke inside. WHAT IS THIS GHOSTLY IMAGE BELOW THIS FURNACE?!?! I don't think we were alone today!

We felt like we explored enough and took off. It was 8 degrees so we decided to make it a short ride. However the ride home was filled with many cool things:
Check out this very unique bike rack. It has rocks in the middle of the wheels. Very cool.
I saw the 1st bald eagle of the season...less than a mile from my house. It was awesome - HUGE, stoic, and majestic.
Some Canadian Geese were out for a spin. Nice formation.

So...can you tell me what that ghostly smoke is in that photo? As if an abandoned sugar beet mill isn't spooky enough! Ahhh - the things you see on a bike ride.