In Ultima Online(1997), there were different tiers of maps “devious, ingenious, etc…” basically T1-T5 if I remember. The higher the tier, the better the rewards. Also harder mobs spawned, which made the rewards even better (as loot/economy was really good in that game). The difficulty was double edged since you would have to either be essentially a tamer (pet dragons) or spend a lot of time summoning blade spirits/energy vortexes that were less effective (as a mage). Or group up with other people (splitting the loot, but adds to the social structure/excitement for groups). Bards were also quite excellent soloers as they could make monsters fight each other.
This also made maps very valuable for trading. One person might find it too much of a hassle and pawn it off to someone more powerful who is hoping RNG swings in their favor to make a profit. You also had to have a cartographer character who was actually trained(takes $$$/time) to actually decipher the map before it reveals the rough location. Lower skilled players could decipher say a T1,T2 but you would need higher skill level for T4 and max level for T5. This portion wouldn’t meld well into current orbus as there are no skills. Unless they added like a cool cartographer table with like pens and magnifying lenses etc lol.
You would then have to figure out the location based off the map, go to it, and attempt digging with a shovel until you strike the correct spot.
The chest was trapped and locked. You would first need to picklock(skill $$$/time) it which the skill level required scaled with the map tier, again. Then it was trapped, and if you triggered it, the damage scaled based off tier again. T5 would kill you 1-shot. There was a remove-trap skill($$$/time again). I also remember people used a spell called telekinesis to remotely open/detonate the trap. It might have been that telekinesis only worked on lower tier traps, and higher traps had to be disarmed.
The mobs spawned as items are looted from the chest as to not immediately crush the player. That means when you take a few items, some amount of mobs will spawn. If you loot the chest dry instead of killing slowly then all of the mobs for that chest would (obviously) spawn. Though you could just have them spawn in waves or over time, etc.
Maps were looted randomly off mobs. To get higher tier maps, you had to kill harder mobs. To get a T5 you had to kill stuff that would basically be group-level combat, or you were a tamer (tamers were OP and a mega pain in the butt to create). T4 would be like difficult but doable content for end game pve’rs. Mobs that dropped T5 could still drop say T4, T3, as T5 was pretty rare. T3 and less was still valuable but less sought after by end-game players. It was a win for everyone. If you looted a map you could easily sell it to another player for good profits. Likewise, the player who enjoyed doing the maps usually profited as well, got good loot from it (like magic weapons, etc) and circulated it back into the economy.
Lastly, you could make treasure-chest exclusive items based off difficulty that would be appealing to go after.
Personally I’ve not seen a better system yet.