This exposition offers a comprehensive guide for players seeking to unlock the subterranean tunnel system within the virtual world of 'Big Walk.' Initially, these vibrant passages, visible across the mountainous terrain, remain inaccessible. The key to activating them lies in the successful completion of a specific architectural challenge, which subsequently enables an efficient underground travel alternative, bypassing the arduous task of scaling steep cliffs. This strategic revelation transforms player movement, allowing for swifter transit across the expansive map.

To gain access to the full network of tunnels, players must direct their efforts towards the yellow tower situated in the northern sector of the game's environment. This landmark is located a considerable distance from the initial spawn point. Adventurous players have the option to trek directly to this tower from the outset. Alternatively, those preferring a less strenuous journey can first conquer the green tower, subsequently utilizing the ski lift feature to reach the northern region with greater ease.

The process of activating the yellow tower involves collecting five distinct gourd-shaped artifacts, which are acquired upon the successful completion of various in-game trials. These collectibles must then be deposited into designated compartments at the tower's summit. Following this, a unique key is provided, which players must then transport to the base of the tower. Here, the key is to be inserted into five scattered keyholes around the vicinity. The final step involves locating a specific yellow tunnel entrance, positioned near the dark tower and beneath the ski lift. Placing the key into this particular entrance triggers the simultaneous activation of all tunnel portals across the landscape.

Upon entering the tunnels, players will discover they are enveloped in darkness. Fortunately, each entrance is equipped with a flashlight, readily available on the ground, to aid navigation. Utilizing these underground routes simply requires entering an opening and following the internal signage, which directs players towards their desired tower destinations. While transit through these tunnels still demands some time due to the game's vast scale, it represents a significant improvement over traversing the challenging, rock-strewn cliffs, where players might frequently encounter obstacles.

Beyond their primary function as rapid transit conduits, these subterranean pathways harbor a variety of hidden surprises. Players are encouraged to embark on thorough explorations of these tunnels to uncover all their concealed secrets and additional features.