Tunnels features an open battlefield surrounded by several rock formations and tunnels that go through said formations. The numerous cave passageways are what the name to this level, Tunnels, is based off of.
Infantry paths: Both bases have a defensive Rocket Emplacement in the middle and a small metal tunnel connecting the infantry production building (Barracks/Hand of Nod), to the vehicle production building (Weapons Factory/Airstrip) to avoid fire while moving around the base.
Both bases also have an infantry path entrance in their base, leading upwards to a wooden bridge that connects towards a nearby promontory facing the field. Infantry can also go downwards to the field via a land ramp. Said ramp can also be used to climb onto the infantry path and either towards the base or the promontory. For GDI, the infantry path entrance lead to the Weapons Factory; for Nod, their infantry path entrance lead to the Hand of Nod.
Both bases also have a small rock cliff facing their main entrances, where snipers can hit the infantry inside the base.
Each base's vehicle cave passageway path branches to a smaller infantry one cave passageway, featuring mining carts and rails. Upon exiting the cave passageway, players will find themselves near the opponent base's harvested Tiberium field.
Lastly, there is a tunnel complex under the center of the rock arch in the middle of the field. It leads to plenty of exits located towards the fields nearby, and provides cover from tank and sniper fire.
Vehicle paths: Vehicles can leave through the front entrance or the back one that leads into a cave passageway. The level is mainly a large field, and vehicles can venture of most parts of the level. There are also two short cave passageways accessible to vehicles under the sides of the rock arch in the middle of the level.
Mystery Crates: Two appear near the harvested Tiberium fields, another two appear nearby the sides of the central rock arch. The last one is directly located beneath the rock arch, and above the small metal tunnel.
Harvested Tiberium field: Each base harvests the field found after exiting from the front entrance.
Tunnels is a large level, so it is best to hold both entrances towards the opponent base with vehicles rather than scatter forces around the field. Forces covering the cave passageway entrance do not have to be at the enemy base itself, they can deny opponent vehicle exit just by lingering around the cave's exit. It is advised to bring Advanced Engineers to keep the vehicles in top shape, since reinforcements will have lots of road to cover before they can merge with the current forces.
An infantry force can hold up at the enemy's base infantry entrance path; still, some infiltrators might be able to sneak out and past from the vehicle paths, especially when vehicles shell each other. It is best to patrol around the base, rather than the infantry paths or field.
Snipers can locate themselves on the cliff found on the front entrance of the opponent base. They can also support vehicles by sniping infantry that happens to be in the open field.
The field it is quite open, but has several rocks, wall parts, and trees scattered around. Still, there will be lots of terrain to cover when running from a rock to another one, and a sniper might spot the infiltrator. There are also a multitude of vegetation and ferns that players might try to blend into in order to avoid getting seen.
Vehicle cave passageways are devoid of any real cover except for some HESCO sandboxes near one side, and infantry cave passageways only have some mine carts that do not provide much cover either. Still, those passageways can hide the player from passing vehicles. The metal tunnel under the rock arch is also a good hiding spot.
Each base has a Guard Tower located in the center of the base, behind the small cliff with the Rocket Emplacement. An infiltrator can reach the GDI Barracks and the Nod Airstrip undetected by the automated defense. It is possible to hide from the tower the back of the other buildings, if the infiltrator manages to reach the spot; they will probably take some fire in the process. It is advised to destroy the Guard Tower prior commencing infiltration missions, albeit the tower being in the center of the base may make it hard to hit with vehicles from outside the base.
Notably, there is a cave behind the waterfall near the Nod base which leads to a plateau overlooking Nod's Tiberium Refinery. Still, the Guard Tower nearby needs to be taken out before infiltrators can jump down and sneak into the base. This additional and subtle entrance is only present for the Nod base - The waterfall near GDI base does not have a cave behind.
Once an infiltrator managed to sneak into the enemy base, they might try to hide in the bunker, albeit it is not recommended as opponent infantry will run around in crowded matches and being in the middle of the base is a bad spot to sneak into a building. Players may also hide in the metal tunnel that each base possesses, but chances of being spotted are high if someone happens to go through there and the tunnels' exits lead towards the front doors of the buildings. Facing the front part of the walls located at each entrance of the base might prove to be a good hiding spot, but exercise caution as players returning back to the base might spot the infiltrator.
Still, each base had some hiding spots: GDI players sneaking into the Nod base can either hide behind the rocks or trees behind the Tiberium Refinery, behind the containers and crates located at the end of the Airstrip's runway, or behind the wall segment and the ramp towards the wall facing the cave passageway entrance, near the Airstrip control tower. Nod players sneaking into the GDI base can either hide behind the HESCO sandboxes located behind the Power Plant, behind the lone tree near the Refinery, or behind the wall segment and the ramp towards the wall facing the cave passageway entrance, near the Barracks.
Stealth Tanks have plenty of space to maneuver in the base, and can linger behind buildings or perch themselves on the wall ramps.
- There is a tiny alcove featuring a skull located in the GDI infantry cave passageway past the vehicle cave passageway.
- There is also a pickaxe stuck on a Tiberium crystal in GDI's Tiberium field.