I don't really see tracking people as an exploration challenge. At least with the rules given it isn't.
I agree, but the majority of "exploration challenges" seem to be built under the assumption that the less information the party has, the better. I disagree.
Ah, most of the time when I've heard people talking about an "interesting environment" they are talking in very broad terms, like "a crystal forest" or "an ancient temple". They rely on the environment being something that is interesting in a cut scene, thinking that is a driver of player engagement.
Maybe an "interactive environment" would be more clear, but I don't think it is a much better descriptor.
Okay, but here we are back to an issue. You have the shack, and you have the clues, but how to the PCs pick up on them?
Generally they would roll investigation right? Well, they have four people, so they are going to use the help action and get advantage. Maybe they have access to guidance or bardic inspiration. If they are high enough level and have a rogue then they might have a minimum result of 10+Investigation mod.
If I as the DM know that they missed the cultists by days, and this shack is abandoned... then they have all the time they need to search it thoroughly. There is no actual challenge in getting this information. In fact, I wonder if I would even have them roll, considering the unlikeliness of them failing.
And, is automatic success interesting? I don't think it always is. So... how do we handle this? We want the PCs to have the information, but a pass/fail die roll isn't helpful, or if they are smart even likely to slow them down.