Best way to get to Vatican Dome climb?

There are not any.

For St. Peters? You still need to go through security to enter the building. I suggest getting there as early as you can. I was there this past March and arrived before 7:30 am. The lines were not long. You can buy a ticket for the dome once there on the left side of the basilica.

Assuming you mean St Peter’s

All waiting in line are waiting to climb the stairs to Dome as well.

Get there early

Thank you. I thought Rick Steves fans would always find a “back door” to everything. I’ll go with early is best, but if everyone goes early…

Not to worry. Everyone doesn't go early. If you arrive between 8 and 9, you'll likely be fine.

The entrance for the dome climb is on the right side of St. Peters. Once you get through security, it is well marked, just before the Basilica portico. Do yourself a favor, and pay the extra for the elevator , it will save you many steps. I've done the climb twice, and while I'm in decent shape, it's a hike, but the view makes the effort well worth it!

Thank you RS people! I’m going in a few weeks! I love to climb stuff.