Combat is harder when you go through an area with traps and environmental challenges where the floor crumbles and you need to cast featherfall, make dex checks, pop some potions, etc...they have what every DM dreams of - being able to build a dungeon that isn't a room with a puzzle, 4 orcs, a pressure plate the closes the walls. In D&D you just cant let a fully rested party be the state they are in for encounters. At some point they need to be drained. Sure, first fight is easy - if you blow your stuff. The fact you know you got 5 more of those fights until you can rest...now its a bit harder.
Think about initiative on this. Its a complex trap from unearthed arcana. I ran it once, it was amazing. The Path of Blades, pg 7-8
https://media.wizards.com/2017/dnd/downloads/0227_UATraps.pdfYou have to change the nature of the party, their fundamental state, as you head into fights because there is so.much.more. to D&D than fighting.
Out of all of this there was only 3 fights. The revenant when you got sucked into a painting, 2 flying swords guarding a treasure, 2 golems that you could deactivate if you figured it out, and the boss. The rest is cursed items, traps, treasure. My players said it was one of the funnest dungeons they've done. They had to *think*. They also had to make con saves when they took a rest because they place was necrotically cold and half the party got exhaustion from their sleep and then had to go through a hall of traps to get to the boss. Yes the name is a joke, and I know it looks crappy it was my DM notes and wasn't made for official presentation. The argument might be made that you CANT do that in games, but you go into initiative on these things and perception checks and investigation checks unlock things like "there are blades" that allow you to misty step past them and try to pull the lever that deactivates them or dispel magic on a magic rune controlling it. I'd wager that not a lot of thought would be needed to implement SOMETHING. Now, after that, pretty beat up. A Monster Manual encounter is now not so easy. Spell slots are blown, HP is down or your potions are and you have a belly ache from eating too many onions.
The issue is the fundamental way the rest system is made couple with this just being fight after fight after fight with very little being creative other than trying to royally cheese the situation after 10 attempts. Its got to be a little more cerebral and diverse.
My 2c

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