When do you go to the silver trench in red rescue team?

In Pokémon Mystery Dungeon: Red Rescue Team, you can access the Silver Trench after completing the main storyline and becoming a Rescue Team Rank of at least Silver. It's a challenging dungeon that requires you to have strong Pokémon and items, as it features a variety of tough enemies and a total of 99 floors. You'll also need to have a special mission that leads you to the Silver Trench, which is related to the Legendary Pokémon Lugia.