Portal Defense: How to Build and Defend Subterranean Bases

To protect your core base from heavy bombardment and aerial strikes in Portal Defense, build a subterranean tunnel network and anchor your primary defensive structures within reinforced cavern systems. Underground positioning forces enemy pathfinding into narrow chokepoints while negating surface splash damage. However, this strategy requires upgrading your power generator to Advanced Tier to prevent unit accuracy penalties and should only be used on maps where portal spawns are concentrated near a single front.

Subterranean Cell Layout and Turret Placement

Organize your underground base into modular, interconnected cells rather than a single long corridor. Modular design allows you to seal off compromised sectors without collapsing the entire defensive front.

• Primary Entry Point: Install a reinforced bulkhead at the tunnel entrance to funnel incoming enemy swarms into a tight engagement lane.
• Turret Alcoves: Place recessed wall-mount turrets along the corridor to achieve 90-degree firing angles and prevent enemies from swarming your hardware.
• Resource Vaults: Position gold and energy generators in centralized, deep-level rooms protected by redundant shielding.
• Support Unit Placement: Anchor Psionic and Musketeer support units deep inside the tunnel network to maintain economy and unit buffs even if surface defenses fail.

Resource Management and Digging Costs

Constructing underground bases consumes more upfront gold than surface building. To maintain progression while expanding deep defenses:

1. Purchase Excavation Efficiency Early: Unlock the Excavation Efficiency upgrade as early in the match as possible to reduce digging costs and expand your footprint without stalling unit summons.
2. Maintain a 3:1 Gold-to-Depth Ratio: Build at least one dedicated resource generator inside a deep subterranean node for every three defensive towers added to your tunnels.
3. Bury Energy Generation: Keep energy generators alongside deep defensive turrets to protect your economy from enemy surface scouts.

Handling Tunneling Enemies and Power Constraints

While underground bases block aerial and long-range surface damage, they introduce specific risks that require targeted countermeasures.