Threshing floors were usually on a high place so that the wind could blow the chaff away.
(The ESV Study BibleTM, English Standard Version (ESV) by Crossway Bibles, 2007. Page 584)
When the prophet Gad advised David to return to Judah, he heard the Philistines were fighting against Keilah and were robbing the threshing floors. David and his men went to Keilah and saved the inhabitants of Keilah. (1 Samuel 23:1-5)
Araunah the Jebusite's threshing floor
It's located on the top of the hill to the north of the city of David, about 450 yards from it. It's the eventual site of the temple.
(The ESV Study BibleTM, English Standard Version (ESV) by Crossway Bibles, 2007. Page 584)
The altar on the threshing floor of Araunah the Jebusite
The LORD sent a plague for three days. When David asked the LORD to let His hand be against him and his father's house, Gad came that day and said, "Go up, raise an altar to the Lord on the threshing floor of Araunah the Jebusite.” David obeyed and bought the threshing floor from Araunah and oxen for 50 shekels of silver. He offered burnt offerings and peace offerings, and the Lord responded to the plea for the land. The plague was averted from Israel.