If "gully" refers to a ravine or channel:
* Ridge: A long, narrow elevation of land.
* Plateau: A large, flat area of land elevated above surrounding areas.
* Plain: A large, flat area of land.
* Hilltop: The highest point of a hill.
* Summit: The highest point of a mountain or hill.
If "gully" refers to a bad shot in cricket:
* Six: A hit for six runs, considered a very good shot.
* Boundary: A hit for four runs, a good shot.
* Good shot: A well-played hit, regardless of the number of runs scored.
If "gully" refers to a term used in cricket for a fielding position:
* Other fielding positions: There are many other fielding positions in cricket, like slips, gully, mid-wicket, etc. The opposite could be any of these other positions.
In general:
* Smooth: A gully is often rough and uneven, the opposite would be smooth and level.
* Elevated: A gully is typically a depression in the land, the opposite would be an elevated area.
To give you a more precise opposite, please provide the context in which you're using the word "gully."