How do you get into the underground in Pokemon Silver?

You can't actually get into the "underground" in Pokemon Silver in the same way you can in Pokemon Diamond, Pearl, and Platinum. There is no separate underground area to explore.

However, you can access the "Underground Path" which is a series of tunnels and caves connected to the main game world. Here's how you get in:

1. Beat the Elite Four and become the Champion: The Underground Path is only accessible after you've become the champion of the Johto region.

2. Find the Entrance: The entrance to the Underground Path is located on Route 40, just south of the Goldenrod City Gym. You'll see a small cave entrance with a sign that says "Underground Path".

3. Enter the Underground Path: Simply walk into the cave and you'll be in the Underground Path.

The Underground Path is a series of tunnels and caves that you can explore. There are some trainers to battle and items to find, but it's not a major area of the game like the Underground in later games.

Let me know if you have any other questions about Pokemon Silver!