What is this????

I was attempting to change the thermostat on my 2001 Dodge Intrepid. I removed what I thought was the housing to find....well, that I didn't really know what I was doing. So, what exactly did I remove(see pictures)? In my frustration, I pryed off the top of this thing and am not quite sure how to put it back on. It almost looks as though there was some type of adhesive holding it down cause I can't find any bolts or fasteners and I don't think I broke anything.....surprisingly. As thoughts would be helpful. I also still have no idea where the thermostat is. I do believe I read something about coming from underneath to get to it. Btw, it's the 2.7L motor.

hope this helps you I was attempting to change the thermostat on my 2001 Dodge Intrepid. I removed what I thought was the housing to find....well, that I didn't really know what I was doing. So, what exactly did I remove(see pictures)? In my frustration, I pryed off the top of this thing and am not quite sure how to put it back on. It almost looks as though there was some type of adhesive holding it down cause I can't find any bolts or fasteners and I don't think I broke anything.....surprisingly. As thoughts would be helpful. I also still have no idea where the thermostat is. I do believe I read something about coming from underneath to get to it. Btw, it's the 2.7L motor.

Turns out it was a coolant air bleeder. No where near the thermostat but I guess it needed to be replaced anyhow since it was leaking coolant.
Thanks for the response.