As far as traps go, the Dungeon Delver feat provides these benefits (PHB, p. 166, 2nd and 3rd bullets) :
- You have advantage on saving throws made to avoid or resist traps.
- You have resistance to the damage dealt by traps.
Does the feat still give resistance to the trap's damage once they're revealed?
Here are a few specific cases:
- An open spiked pit is found. Does the delver still get resistance to the trap if he knowingly tries to jump over it?
- A Wall of fire is triggered from a Glyph of Warding spell. Does the delver still get resistance to the fire if, several seconds after the spell is triggered, he knowingly passes through the wall?
The source of the hesitation is the wording of the feat's description:
Alert to the hidden traps and secret doors found in many dungeons, you gain the following benefits [...] (emphasis mine)
In other words, one might think that once a trap is revealed, and it's effects known, it's not a trap anymore, but a mere feature of the terrain, thus restraining the reach of the feat.
As a player, one would like to know so before choosing the feat; as a DM, another might want to know how to deal with delvers hurling themselves in harm's way saying: "Don't worry! That 60 foot deep pit was once meant as a trap... I should get only half of that falling damage!"