Here's how to find and customize your secret base in those games:
1. Find a Secret Base: Look for glowing spots on the overworld map, particularly in areas like forests, caves, and mountains. These spots will mark the entrance to a secret base.
2. Enter the Base: Interact with the glowing spot to enter the base.
3. Customize Your Base: Once inside, you can customize your base with various decorations and items. You can also place traps to challenge other players who might visit your base.
4. Connect to the Wireless Network: To share your base with other players, you'll need to connect to the Wireless Network. This will allow you to find other players' bases and challenge them to battles.
If you are playing Pokémon Diamond, you won't be able to create or visit secret bases.