Hidden island

Hidden islands are islands that are shrouded under fog which need to be unlocked in order to gain access to them. By default, hidden islands are only available in Isla Paradiso, although there's a method to create custom hidden islands.

There are a total of 8 hidden islands around Isla Paradiso, and each of them can be unlocked in different ways. Once a hidden island is revealed, the fog will recede and the island will be owned by the Sims who discover it. The island will become the Sim's secondary home, or it can be turned into a resort. Below is the method how to unlock them.

Plumbob Island
Sims need to find a message in a bottle containing the map of Plumbob Island. This message in a bottle is an extraordinarily unusual collectible, which can be found with a seashell spawner. Once Sims find the map, the island will be unlocked.

In the island itself, there's a treasure chest that contains §3,333, a large PlumbBob cut Rainbow gem, and the "Evolution of the Plumbob" painting worth §12,121.

Cay to the City
To unlock this island, Sims must rescue 35 drowning Sims in Lifeguard profession.

No Trouble Atoll
To unlock this island, Sims must reach the 5-star rating of a resort.

Refuge Island
This island is unlocked by completing a series of chain opportunities. Sims can get the opportunity by checking in a resort and asking the front desk for an adventure. There's a total of 6 opportunities to be completed.

On the island, there's a small shack and a fishing spot.

Beryl Shoals
Sims only need to swim or boat to this island to unlock it.

Mermaid's Secret
Sims need to become good friends with a mermaid. After that, meet them in a diving area, and they will show the way to the island.

Diver's Den
Sims require to master the Scuba Diving skill in order to unlock this island. One of the exit routes of the underwater caves will lead to the hidden island. There is a treasure chest on the shore that contains 1,200 simoleons, gold, iron, palladium, and silver.

Plunder Cove
To unlock this island, Sims need to discover 4 map pieces around the town. The map pieces can be found in the treasure chests or from a message in a bottle. After Sims possess 4 of the map piece, they can reconstruct it to unlock the hidden island. Additionally, Sims can purchase the Uncharted Island Map lifetime reward to instantly unlock this island.

The island has a treasure chest that contains §1,200; Blue Topaz, Tanzanite, Emerald, Smokey Quartz, Yellow Sapphire and Ruby gems.