Old Sea Map is an item in the “Event items” category (Key Items).
In-game descriptions
| Emerald | A faded sea chart that shows the way to a certain island. |
|---|
Where to find it
Not placed on the atlas maps (so far: Red/Blue and Generation 3).
Sources : PokeAPI (items, item_flavor_text, machines) · atlas · pokeemerald species_info.h