It's a recording of birds singing on a swamp inside a forest near an underground service station.
You can hear lots of birds chatting around, the place was crowded with them. Once in a while a fly passes by. There's some mechanical noise in the background at the end of the recording. You can also hear me come and pick the recorded at the end.
Recorded with Zoom H2: WAV, 96kHz/24bit. I used rear mics, they were pointed to the sky, with a slight tilt. I was hoping to get most birds and less other stuff. It was normalized, panned and edited with Audacity.