From the Super Mario Wiki
A typical hole from Boo Valley
Boo Valley is a golf course that appears in Mario Golf, for the Nintendo 64 and Mario Golf. The course is located in a valley inhabited by Boos, hence the name. The course is fairly large at 6,635 yards (6 067 metres). Bunkers are rare and there are only two water hazards in the course. However, due to the number of cliffs, it is very easy to hit the ball out of bounds. When choosing this course in tournaments, "Boo Classic" is mis-spelt as "Boo Clasic".
The course also re-appears as a downloadable course in Mario Golf: World Tour, this time being based on Rock Candy Mines.