The Hold is the name of the first, tutorial location available in the game, that the players start on their adventure. It's a smal three-deck prison ship that transports sourcerers to Fort Joy and where the Troubled Waters quest takes place.
In the Definitive Edition of the game, an additional tutorial deck has been added (not included on the map below) that allows new players to familiarize themselves with the basic controls, etc. You can learn here how to move objects, unlock doors with a key, a lever, the lockpicks or the pressure plates, learn about surfaces and their effects, learn about scrolls, use beds, fight the first fight or get some items and gold.

Locked Passages x3, Keys x2, Future Party Members x7, NPCs x5, Chests x5, Fight x1, Transitions x6, Other x2
An alphabetical list of quests that begin on this map.
The following legend of The Hold interactive game map defines the points of interest / markers displayed on the map. Each marker corresponds to a specific element to facilitate efficient navigation and interaction with the map.
Closed door, gates, etc. Mostly they will need a key or high lockpicking skill to open them, but some, these with low HP, can be opened by force.
They can't join your party yet, but this will be possible at the later stages of the game, in Fort Joy, etc. It does not matter if you come back to save them at the end of the Troubled Waters quest. In both cases they will survive.
Places where you will surely have to fight against the opponent(s).
Transitions between map levels, locations, etc.