How do you get a nevermeltice in ruby?

In Pokémon Ruby, you can obtain a Never-Melt Ice by exploring the area known as the Icefall Cave. Inside the cave, look for a hidden item on the ground near a waterfall. Use the move Surf to navigate the water and find the item, which is the Never-Melt Ice. This item boosts the power of Ice-type moves when held by a Pokémon.