Forgotten Altar
Forgotten Altar is an Act 2 event where the player discovers an ancient altar. They can offer a relic (lose one relic, gain 25 max HP and have all non-relic HP increased temporarily), offer HP (lose 25% max HP and receive a random relic), or offer nothing and leave. The altar has no combat.
Forgotten Altar's value depends entirely on your relic inventory and HP situation. Offering a weak relic for 25 max HP is a good trade if you have a dispensable relic. Offering HP for a random relic is worthwhile if you are at high HP and need a relic more than max HP. Leaving the altar is always an option with no penalty. The key consideration is whether your least valuable relic is worth 25 max HP, or whether 25% max HP is worth a random relic.