Fifth Element
Legend
Or you could just read the DMG. From page 261:Mental gymnastics might allow noncombat encounters to award experience
"NONCOMBAT CHALLENGES
You decide whether to award experience to characters for overcoming challenges outside combat. If the adventurers complete a tense negotiation with a baron, forge a trade agreement with a clan of surly dwarves, or successfully navigate the Chasm of Doom, you might decide that they deserve an XP award.
As a starting point, use the rules for building combat encounters in Chapter 3 to gauge the difficulty of the challenge. Then award the characters XP as if it had been a combat encounter of the same difficulty, but only if the encounter involved a meaningful risk of failure.
MILESTONES
You can alo award XP when characters complete significant milestones. When preparing your adventure, designate certain events or challenges as milestones, as with the following examples:
- Accomplishing one in a series of goals necessary to complete the adventure.
- Discovering a hidden location or piece of information relevant to the adventure.
- Reaching an important destination.
There you go, guidelines for awarding XP for non-combat encounters, right in the core book for the DM. No mental gymnastic required; it's in the rules.