Throughout every level, there are numerous secret areas hidden away from the main path. These often contain valuable power-ups like Serious Damage (doubles your damage output for a limited time), Invulnerability (makes you immune to damage for a short period), or large health and armor bonuses. To find them, look for:
- Suspicious Walls: Walls with cracks, different textures, or slight indentations often hide secret passages. Shoot or melee them to reveal the entrance.
- Hidden Ledges: Areas that seem inaccessible might have invisible platforms or require precise jumps to reach.
- Environmental Puzzles: Sometimes, activating a specific switch or destroying a particular object will open a secret door elsewhere.
- Out-of-Place Objects: A single barrel in an empty room, or a strange rock formation, can sometimes mark a secret.
Exploring these areas is highly recommended, as the power-ups can turn the tide of a difficult battle. Many secrets also contain large caches of ammunition for your most powerful weapons.