[1] The island is just beyond the upscale suburban construction of Nesøya, reachable across the Vendelsund sound by cable ferry during the summer and a pontoon bridge in winter.

The etymology of "Brønnøya" (variously spelled Brøndøen, Brønnøen, Brunneyr, Brunøen, Bryøen, Brundøen, and Bryndøen) stems from the presence of wells (Norwegian: brønn) on the island, the source of water with an unusual ability to stay fresh in storage.

In the late 16th century, bishop Jens Nilssøn recorded that a well (now empty) on the eastern side of the island is said to have been identified by the presence of the Virgin Mary and still has the name Mariakilden.

[1][2] Remains of two Nordic Stone Age settlements have been found on the island that may stem from 4000 BCE (when the tide was 40–50 meters higher than today), and there are traces of agricultural activity going back at least 1500 years.

A number of other requirements were also established, including minimum lot size (2 metric dunams), and common areas.

[2] Although there is a general consensus that the island needs to maintain its unique character, there have, broadly speaking been two camps that have opposed each other on the means for preservation.

Some favor a permanent bridge to ease access; others feel this is a slippery slope toward allowing automobiles on the island.

[2] By 1928, when Myhre and Monsen started selling lots, the public road to the southern end of Nesøya was also complete.

[2] In 1953, the nursing home on the island was acquired by Jens H. Koefoed, who was impressed by the cable ferry between Ormøya and Padda in Oslo.

This worked well when the sound was frozen, but when the ice thawed and broke, pedestrians usually had to run across the bridge to stay dry.

The municipality expropriated the lot needed to build a walkway from the bridge landing to the road on Nesøya, and the harbormaster approved the use of the cable ferry.

Replacing the barrels that sprung leak became an urgent but arduous routine, and the ferry was not able to handle pedestrian traffic at peak periods during the summer.

In 1973, Jak Haukvik, one of the island's long-term residents, engineered a new cable ferry based on a raft, rather than, boat design.

Service between Sandvika and Brønnøya between 1948 and 1968 was provided by Einar Andersen, who shuttled passengers on board a retired lifeboat (from Stavangerfjord) starting at 5:30 am until 10 pm.

There are several nature reserves on the island, including Viernbukta, where grey heron are sighted[5] Commonly seen plants on the island include: Valeriana sambucifolia, Geranium sanguineum, Geranium robertianum, Lotus corniculatus, Sedum acre, Hylotelephium maximum, Silene vulgaris, Silene uniflora, Potentilla erecta, and others.

Some want to make it more accessible for a larger share of permanent residents and more tourist and weekend traffic; others feel that it should remain somewhat remote and protected.