The Acheron road through Molesworth Station - which is normally closed to the public - is open for the summer.
New Zealand's largest farm covers 180,467 hectares and the route is open only a few months each year.
The Department of Conservation says the six hour scenic drive between Blenheim and Hanmer Springs will stay open until April.
DoC says 7500 people make the trip through Molesworth station each year.
It warns drivers to be careful on the narrow, unsealed road and says there is no cellphone coverage.