For the International Church of Cannabis in Denver, there were three reasons to celebrate on Thursday.
First, it was opening day. The church, a more than century-old building recently adorned with brightly colored paintings by the artists Kenny Scharf and Okuda San Miguel, welcomed the public early in the afternoon, at which time no cannabis consumption was allowed inside.
Second, it was April 20, an unofficial holiday of sorts for marijuana users. There have been disagreements as to why the number 420 has taken on significance in the cannabis community, but Steve Berke, the church’s media relations director, did not want to worry about that.

Works of art by Kenny Scharf and Okuda San Miguel adorn the interior of International Church of Cannabis in Denver.
“It’s a number that everybody’s adopted, and we’re adopting it too,” he said. The church closed its doors to the public after 2 p.m. local time, leaving only invited visitors, who were allowed to light up for a private 4:20 ceremony.
And third: A challenge to the church’s legality, in the form of an amendment proposed in the state’s House of Representatives, was shut down almost as quickly as it arose on Thursday morning.
“It seemed to be a nice steady flow of people,” said Lee Molloy, a founder of the church and a member, who estimated that a couple of hundred people had come by.
All told, it was a good day for the church’s membership, which ballooned to more than 200 people from around 50 this week after increased media attention.
Colorado legalized recreational marijuana in 2012 and has been fine-tuning its regulations ever since. It is still illegal to smoke in Denver’s public spaces. And some decisions on legal usage are still left up to cities, creating a patchwork of laws that legislators are still working to consolidate.

The church’s media relations director, checked the ages of visitors to the church on Thursday.
Mr. Berke and Mr. Molloy are founding members of Elevation Ministries, the religious nonprofit behind the church. “We thought we could do something different, something unique,” Mr. Berke said, explaining that the church adheres to no specific dogma.