Thales had always had what one might call a scientific curiosity regarding the dungeon. Or, more accurately, they had a scientific curiosity regarding the entirety of the world. It just so happened that the dungeon was an influential part of this world.

Yet scientific study could be done at a distance, so that alone would not be the answer. 

Back in the beginning, while other foals pranced and played games, Thales observed and studied everything they could get their hooves on. They would have been the odd one out, in all likelihood, if not for a fellow foal known as Creed.

Creed was an anomaly to Thales, and therefore was extremely interesting. He had been found in a dungeon by an adventurer, which while interesting was not an anomaly on its own so far as things went. At least three unusual qualities had to be attached to anything for Thales to consider that specific thing an anomaly.

Of course, Creed had to be an overachiever in this regard. Thales prided themself on their ability to keep track of data, yet the unusual details of Creed were countless. Usually such words were deemed by Thales as exaggeration, but Creed himself proved that wrong through showing at least three unusual qualities before noon each day.

Having known each other since they were both foals, it made a logical sense that if such a pattern persisted then Thales would eventually lose count. At first, Thales had assumed an exponential decrease in unusualness would occur, back when they were young. There were only so many years one could believe that for.

So Creed was an anomaly, to say the least, and when followed to the source, it seemed the oddity of Creed had to be related to the dungeon, the same place where he came from.

Somewhere along the way of researching Creed, the two horses had become partners of some kind or another. Thales insisted they were science partners, when asked to specify. Meanwhile, Creed called them adventuring partners. 

(Others called them a pair of idiots perfectly suited for each other.)

In any case, it had been less that Thales had answered the call of the depths on their own. Rather, they had followed Creed as he did that instead, completely unwilling to let this most odd of anomalies out of their sight. 

As for when, the two had both barely been grown when they started researching and adventuring. In many ways, they were still barely grown, constantly learning this world of dungeons. But that was a study for another day.