Thirty-ninth Training Grounds
The thirty-ninth training grounds is the location of the second portion of the Konoha Chuunin exams, a battleground meant to train chuunin on the particulars of combat in shore-side villages or river towns. A large river passes right through the middle of the training ground where a large majority of wooden and sheet-metal buildings have been built up on stilts for when the river floods in the spring. The only building of particular note is a large stone tower situated on an island in the middle of the river, the observation tower where chuunin, jounin, or even the Hokage would observe the practice runs of chuunin using this training grounds. It stands heads and tails above the other buildings and trees of the training ground and is an easy source of reference for those within it.
Generally the river bank and buildings have various insidious traps around them, part of the specialized combat training that chuunin use this training grounds for, but the traps aren't the only source of danger and some consider them to be the least. The other hazards of the thirty-ninth training grounds is the myriad of dangerous animals and planets that rightfully call the fenced in area 'home' and count among their number large crocodiles (and similar amphibious reptiles), poisonous snakes of various size, massive venus fly-traps, and ravenous fish and crustaceans inhabiting the riverbanks and the river itself. While a chuunin would find the training ground a challenge to get through, for those less experienced in the shinobi would find the swampy training zone hazardous at best and fatal at worst.