How can my players gain long-term resistance against a specific damage type?

Question

My players are exploring a megadungeon. They're close to encountering a section of the dungeon where ancient elemental spells have run amok and do constant area damage. Specifically, in some areas in this dungeon, players will take 5 damage of an elemental type (fire, cold, lightning, or sonic) each round.

The intent is that these areas of the dungeon are essentially inaccessible unless the players obtain resistance to the specified damage type. They've previously met a potion merchant who sells potions of lesser resistance, so they'll be rewarded if they remember that and go buy lesser potions of resistance.

However, I'm curious what other options players have to solve this problem. Are there other spells, items, or effects that give long-term resistance to a specific damage type? Note that they'll need resistance for a minimum of 10 minutes, and ideally 30-60 minutes, to give them time to explore, solve traps, and figure out how to fix or disable the spells. This means that spells or effects that give one minute of resistance will be insufficient, and effects that give 10 minutes of resistance may not work unless they are relatively low-cost and could be reapplied.

Answer 1

Magic items

You already covered potions of resistance, which are probably the cheapest option if they do not need to spend multiple hours in there.

• The Ring of Energy Resistance will give the wearer permanent resistance 5 for one energy type at a price of 245 gp. It is invested so there is a limit to how many you can wear, but you could potentially wear multiple to get resistance from all four types. They would need enough funds and a source to buy them from.

• A Broadleaf Shield at a cost of 225 gp can, depending on the season, give durable resistance of 6 to fire or cold when it is raised; so only a partial solution.

• Energy-Resistant runes can be etched on armor and provide permanent resistance 5 to cold, fire, lightning (but not sonic). Cost is 420 gp per rune.

Spells

• The aptly named Resist Energy provides your stipulated minimum 10 minutes of resistance 5 to any of the energy types for 1 creature, and as a level 2 spell is relatively affordable.

• The 7th level spell Energy Aegis provides resistance to all those damage types for a whole day for 1 creature.

Other tactics

If they only need to get through those areas, non-resistance tactics might also work. For example, they could use the uncommon spell Painted Scout to scout the area, and once they found the other side of the danger area, Teleport there.