What was the purpose of that big hole in the ground in Episode I, where Darth Maul fought Obi-wan and Qui-Gon? And why was it defended sa pamamagitan ng multiple laser doors?

Probably was a big reactor of some kind. The hole was a cooling vent, and the laser doors were so no one would risk going in. They probably alternated due to power shortages.

it was a power generator.