Sons of the Forest Building, Caves and Bunkers Guide

Sons of the forest building isn't just placing walls; it runs through a blueprint-and-complete system built around Kelvin, the game's AI companion, plus a separate keycard-gated bunker network that's easy to conflate with the game's regular caves. This guide covers all three pieces using only what the official wiki and Steam's own patch notes confirm.

TL;DR: Sons of the Forest has 78 confirmed prefab buildings, placed as blueprints that Kelvin can complete on command. Kelvin's confirmed orders span gathering, building, and base maintenance. Virginia is a separate, recruitable companion won over through patience rather than force. Caves (9 marked, plus the unmarked Hell Cave) are mostly tool-gated; bunkers are a distinct, keycard-gated network hidden from the GPS until found.

How does building actually work in Sons of the Forest? (quick answer)

Players place a blueprint, a ghost outline of a structure, and either build it themselves or assign Kelvin to complete it. The official wiki's Kelvin page confirms he "builds shelters, fires, and completes structures from player blueprints," and a January 15, 2025 Steam patch specifically added a procedural defensive wall placement system: "you can now just draw out where you want the walls and let Kelvin finish them." The wiki doesn't document the exact step-by-step placement UI beyond the blueprint-then-complete flow, so this guide sticks to what's confirmed rather than guessing at menu specifics.

Key takeaways

• 78 confirmed prefab structures, numbered on the official wiki's Prefab Buildings page
• Kelvin can complete blueprints, build fires/shelters, and (per an update) finish all buildable structures in an area automatically
• Virginia is a separate companion mechanic: recruited through patience, not combat
• 9 marked caves plus 1 unmarked Hell Cave, mostly tool-gated
• 7 named bunkers, keycard-gated (Maintenance, Guest, VIP) and hidden from GPS until found
• A "nail gun" as a building tool could not be confirmed on the wiki's Tools page

The 78 prefab buildings

The official wiki's Prefab Buildings page lists 78 numbered structures a player can place as blueprints. These range from basic survival shelters (Hunting Shelter, Log Cabin, Lean-to, Tree Platform, Tree Shelter) to furniture and storage (Stick Chair, Double Bed, Log Storage, Weapon Rack) to functional traps (Spring Trap, Molotov Tripwire, Explosive Tripwire) and utility items like the Rain Catcher. That range matters for planning: a base built purely around shelter prefabs looks and functions very differently from one that also incorporates the trap-focused blueprints, and the wiki's own numbering (1 through 78) makes clear this is a substantially larger system than the handful of shelter types a new player typically encounters in the opening hour. Most players only ever place a fraction of the full list across a single playthrough, which is worth knowing if you're wondering whether you've "seen everything" the building system offers after just one base.

Bunker interiors use enclosed, human-built rooms rather than the open forest terrain most prefab structures are placed in.

Kelvin: what he can actually be ordered to do

Kelvin is a mute AI companion whose confirmed order list, per the official wiki, includes: Take Item, Follow Me, Get (Berries, Fish, Sticks, Rocks, Stones, Arrows, Radio, or Logs), Build (fire, shelter, finish structure, or clear shelter), Stay (here, at shelter, or hidden), Take a break, Maintain base, and Clear (5, 10, or 20 meters). Patch-note history on the same wiki page adds further confirmed orders over time: Reset traps, Fill log sleds, Fill drying racks with fish, and a "Return to shelter" order that also sends him back to hunting shelters or beds. The "Finish Structure" order was also updated at one point to complete all buildable structures in the area before stopping, rather than one blueprint at a time.

What Kelvin's command list does NOT include, based on this same source, is any direct combat order. He's built around gathering, building, and base maintenance rather than being assigned to fight, which is worth knowing before relying on him as a defensive plan. A base built around Kelvin's automation still needs the player, or Virginia once she's befriended, to handle any actual confrontation that reaches the perimeter.

GODEEPER: None of this building infrastructure matters much if you can't survive long enough to use it, and the game's three confirmed boss fights are the sharpest test of that. Sons of the Forest Bosses: All 3 Explained →

Virginia: the companion, not the boss

Separately from Kelvin, Virginia Puffton is a recruitable companion confirmed on her own wiki page. She starts wary and skittish, and the player has to slowly earn her trust through kind, non-threatening interactions rather than forcing the relationship. Once that trust builds, she brings small gifts (berries, aloe vera, rocks, sticks, animal remains) as tokens of gratitude, signals the player toward points of interest like camps and loot spots, and will fight alongside the player against threats once armed and befriended. Poor treatment can permanently lose her from the game (scared off, ignored, or killed), so this isn't a companion that can be recruited carelessly and expected to stick around regardless of how she's treated.

Caves versus bunkers: two different systems, easy to conflate

Sons of the Forest has two separate underground exploration systems, and conflating them leads to some of the more confusing secondhand advice about the game. Caves are the more common system: 9 marked locations that show up on the GPS immediately, plus one additional unmarked location called the Hell Cave. Progression through a cave is mostly tool-gated rather than key-gated: reaching further sections might require the Rope Gun, or the Rebreather for flooded areas, and at least 2 mutants respawn daily per cleared area.

Cave interiors reward exploration with loot, mechanical progression items, and story content, gated mostly by tools rather than keys.

Bunkers are a genuinely different system. The wiki lists 7 named bunkers: Food and Dining, Entertainment, Residential, Luxury (accessed via a control panel inside Residential), and Maintenance A, B, and C (digsites that need a Shovel to reach). Bunker access is keycard-gated using a Maintenance Keycard, Guest Keycard, and VIP Keycard, and bunker entrances stay invisible on the GPS until the player finds the corresponding GPS laptop that reveals them. Confusing a cave for a bunker (or vice versa) in planning is an easy mistake given how similar the exploration loop feels moment to moment, but the actual gating mechanics behind each are not interchangeable.

Low-visibility cave sections like this one are common across both the standard caves and the Hell Cave.

Frequently Asked Questions

How many prefab buildings are in Sons of the Forest? 78, confirmed and numbered 1 through 78 on the official wiki's Prefab Buildings page. Examples include the Hunting Shelter, Log Cabin, Look Out Tower, and several trap types.

What can Kelvin build in Sons of the Forest? Kelvin can complete player-placed blueprints, build fires and shelters, and (per an update) finish all buildable structures in an area before stopping, based on his official wiki-documented Build command options.

How many caves are in Sons of the Forest? 9 marked caves that appear on the GPS, plus one additional unmarked location called the Hell Cave, per the official wiki.

How do bunkers differ from caves in Sons of the Forest? Bunkers are keycard-gated (Maintenance, Guest, and VIP keycards) and hidden from the GPS until a corresponding laptop is found, while caves are GPS-marked from the start and mostly tool-gated, requiring items like the Rope Gun or Rebreather.

Is Virginia a recruitable companion in Sons of the Forest? Yes. Per the official wiki, she starts wary of the player and must be slowly won over through non-threatening interactions before she'll bring gifts, guide the player to points of interest, and fight alongside them once befriended.

Can you order Kelvin to defend the base in Sons of the Forest? Not as a direct combat order. His confirmed commands center on gathering, building, and maintaining the base rather than combat, including reset traps, fill drying racks, and maintain base.

Related Reading

• Sons of the Forest Complete Guide: the hub for every Sons of the Forest guide on this site.
• Sons of the Forest Bosses: All 3 Explained: the confirmed boss roster and why Virginia isn't one of them.
• Sons of the Forest Weapons Guide: All 21 Confirmed: every melee and ranged weapon, useful for defending whatever you build.

References

• Sons of the Forest on Steam: official store page and current review data.
• Sons of the Forest official wiki: Prefab Buildings: the full 78-structure list.
• Sons of the Forest official wiki: Kelvin: confirmed command list and patch history.
• Sons of the Forest official wiki: Bunkers: keycard system and named bunker list.