Climbing
Source: Player’s Handbook (2024) p. 363. Available in the SRD and the Free Rules (2024)
While you’re climbing, each foot of movement costs 1 extra foot (2 extra feet in difficult terrain). You ignore this extra cost if you have a Climb Speed and use it to climb. At the DM’s option, climbing a slippery surface or one with few handholds might require a successful DC 15 Strength (Athletics) check.