This lot hs been in the same family for generations. No engineering work has been done. It's raw land. Some of the permitted uses by right in RA3 are as follows. There are several more available by a special use permit as well, as noted below.
Single-family dwelling
Agriculture
Farm
Conservation uses
Forestry management
Private stable
Class 1 home occupation within the principal dwelling
Customary residential accessory structures/uses
Ground-mounted solar under 400 sq. ft.
Certain residential subdivision configurations, including conservation-density and cluster development.
Uses possible with a Special Use Permit

RA3 actually allows a fairly broad range of uses with Planning Board approval and, in many cases, site-plan approval are obtained. Some potentially valuable ones include:

Boarding stable
Riding academy
Golf course/country club
Hunting/fishing club
Private outdoor recreation facility
Bed-and-breakfast with more than two guest rooms
Inn
Conference center
Church/place of worship
Day camp
Educational institution
Museum/library
Nursery school
Elderly/senior housing
Enriched housing for the elderly
Class 2 home occupation
Roadside stand
Commercial timber harvesting/logging
Extractive operation/soil mining, subject to significant approvals
For example, a riding academy is specifically an SP use in RA3, as are boarding stables.