Which of the following is NOT a valid reason people choose to cave dive?

Exploring human-created structures is typically associated with activities such as urban exploration or wreck diving, rather than cave diving itself. Cave diving focuses primarily on natural underwater environments formed in limestone or other soluble rock types. The allure of cave diving usually revolves around the exploration of natural phenomena, including the unique geological features and ecosystems present in underwater caves.

In contrast, the other options present valid reasons for participating in cave diving. Many divers are drawn to the intricate beauty and formations found in caves, such as stunning stalactites and stalagmites or clear underground water. Additionally, the fields of hydrology and geology play a significant role in attracting divers who wish to expand their understanding of water systems and earth formations. Lastly, while challenging logistics can be a part of the experience, this aspect is often viewed as an appealing challenge rather than a deterrent, reinforcing the adventurous spirit of cave divers.