After earning the good ending in Castlevania: Portrait of Ruin, you will still be able to continue exploring the map and completing any remaining quests or tasks. The good ending does not restrict your ability to continue playing the game in any of the available modes, including the main mode (Jonathan mode) on Hard difficulty.

Here are the steps to ensure you can continue exploring and completing the map:

1. Defeat True Dracula: To unlock the good ending, you need to defeat True Dracula. This is a requirement for accessing certain modes and difficulties.

2. Access Various Modes: With the good ending, you will gain access to modes such as ‘Sisters’, ‘Richter’, and ‘New Game +’ Modes. These modes allow you to play through the game with different characters or with increased difficulty levels.

3. Explore the Map: You can continue to explore the map and complete any remaining quests or tasks. This includes finding hidden items, defeating specific enemies, and unlocking secret areas.

4. Complete Wind Quests: If you have not completed all the Wind quests, you can still do so. These quests include tasks like defeating specific enemies, collecting items, and completing various challenges.

5. Play on Hard Difficulty: If you want to play on a higher difficulty level, you can do so in any mode, including the main mode on Hard difficulty. This will provide a more challenging experience but does not restrict your ability to explore the map.

In summary, earning the good ending in Castlevania: Portrait of Ruin does not limit your ability to continue exploring the map and completing any remaining quests or tasks. You can continue to play through various modes and difficulties, ensuring that you can fully experience the game’s content.