My party is currently doing a mini-dungeon crawl before they arrive at the fight against one of the three big bads of the campaign. I have set up small challenge rooms specific to each party member - they are optional rooms that only one character may enter. If they pass the room's challenge, they get an advantage over the big bad and if they fail there are no real consequences. The rooms are designed to play to their specialised skill so it feels really personalised and like 'only they could complete it'. 

The room I have built for the rogue is a long dark corridor that has roaming cctv casting light - the challenge is to stay hidden until they reach the end. The room for the druid is a large body of water that is filled with sharks - they have to blend in with the sharks long enough to find the right key hidden at the bottom of the lake. The room I have for the wizard is a magic storm situation - they have to maintain concentration whilst trying to nullify area of effect spells. 

I'm struggling to think of a room specific challenge for our Paladin and for our multi-classed Ranger/Rogue. There's been a bit of tension between the two rogues doing the same job before so I want to make sure the two rooms are distinct and it plays into their Ranger class more. And Paladin I have no idea what kind of non-combat specialised challenge they would need to face. 

Anyone got any suggestions?

Ranger/Rogue: Navigate a very hard-to-follow trail (Survival skill challenges). Any failures lead the character into a fauna-based trap (Nature and Sleight of Hands skill challenges to avoid/disarm).

Paladin: The challenge of Mercy. They find themselves in a situation where a hostile crowd of folks is desperate for the Paladin and another NPC warrior to have an honor duel. The Paladin can easily tell that the other warrior is afraid and not up to the challenge (Insight) and states that the "right thing to do" is to either negotiate a non-fighting result or to honorably not allow any resulting fight to end in death. That's some religion, possibly "The gods do not favor this behavior," and/or deliberately letting the other person have first blood.

I like Agile_DM's suggestion. I'd also say that, if you wanted it to be less RP-challenges and more of skill based, you could have the Paladin challenge be something that makes use of their Aura of Protection (assuming they have a decent charisma). A paladin would have a much easier time succeeding on saving throws, which could be a fun thing to go with. 

Or possibly it could be that the player has to deal a certain amount of radiant damage every turn to destroy some evil artefact.

Or maybe combine those ideas, and have them need to make a saving throws after dealing damage until it's destroyed. 

Nice ideas up above.

Your Paladin could do a save the baby task. They see a snow covered village with a building on fire. Within the building there is a child that needs saving. Stay alive while taking fire damage, heal the child if they take fire damage, choose more damage going back to the first floor or jump off the upper floor of the building.