Secretary of State Mike Pompeo headed to Europe on Thursday as part of another bid to build support for the U.S. government’s pressure campaign against Iran.

But there is one stop en route that is sure to interest those who are more conspiratorially minded: Pompeo’s side trip to the secretive Bilderberg Meeting.

The State Department has said that Pompeo is planning to briefly stop by the elite event, held this year in Montreux, at some point during a three-day stay in Switzerland. He is not the only senior U.S. official visiting, either — Jared Kushner, President Trump’s senior adviser and son-in-law, is listed as an attendee on the meeting’s website.

The involvement of key Trump administration members may spark criticism from those who view the meetings as nefarious gatherings of the global elite. Conspiracy theorists, including a number who have publicly supported Trump, have picketed the event in recent years.

For example, Alex Jones, the American radio host who interviewed Trump when he was a presidential candidate in 2015, has claimed that Google “planned and launched” the Arab Spring at one such Bilderberg gathering.

“There are powerful corporate groups, above government, manipulating things,” Jones said in 2013 in Britain, where he was filmed standing outside the site of that year’s Bilderberg event.

People who have attended the meeting say that there is little to these theories and that it is just a forum for honest and open debate. However, Bilderberg’s long history, unusual levels of secrecy and A-list guests certainly make it an unusual event.

How did the meeting begin?

The event dates to 1954, when a small group of powerful Europeans met with a group of influential North Americans to discuss the future of the transatlantic liberal alliance.

The event, convened under the leadership of Prince Bernhard of the Netherlands, was first held in the Bilderberg hotel in Oosterbeek. The meeting has since occurred almost every other year, in locations as far west as Lake Lanier, Ga., and as far east as Istanbul.

The only year a meeting wasn’t held was in 1976, when it was canceled as Bernhard was embroiled in a scandal over accusations that he took a bribe from U.S. aircraft manufacturer Lockheed.

Who attends?

The known list of past attendees is vast. A number of them have gone on to lead nations shortly afterward: Angela Merkel attended in 2005, only months before becoming the German chancellor, while Bill Clinton attended in 1991 when he was still governor of Arkansas.

Serving world leaders have also attended: Margaret Thatcher attended at least once while she was Britain’s prime minister.

It is relatively unusual for a serving U.S. secretary of state like Pompeo to attend, though not unprecedented: Condoleezza Rice was listed as a participant in 2008, when the event was held in Chantilly, Va., while she was still head of the State Department.

Nor are Pompeo and Kushner the first Trump administration staffers to attend: In 2017, when the event was held again in Chantilly, administration officials including Commerce Secretary Wilbur Ross and national security adviser H.R. McMaster attended.

About 130 attendees come every year, with two-thirds generally from Europe and one-third from North America. A third are in government and politics, and the rest are from other fields.

The 2019 attendee list includes many core participants, such as former secretary of state and national security adviser Henry Kissinger, but the organizers make an effort to include fresh faces, too: Stacey Abrams, a rising Democratic politician from Georgia, is listed.

Why is it so secretive?

Participants at the Bilderberg Meeting are barred from revealing who said what during discussions under Chatham House rules, and the group does not release any notes or summaries of discussions. Journalists are not allowed to report on the event, though some attend as participants.

The organizers say this isn’t about secrecy but privacy. Participants are asked to speak openly at the event and not be bound by the constraints of their office or fear that they will make headlines. Bilderberg’s sparse website notes that the meeting used to hold news conferences every year up until the 1990s, “but it was stopped due to a lack of interest.”

Since then, however, the perceived secrecy has fueled conspiracy theories. In interviews, organizers have said it is a cost the group has to bear.

“It is unavoidable and it doesn’t matter,” Viscount Etienne Davignon, chairman of the Bilderberg group at the time, told the BBC in 2005. “There will always be people who believe in conspiracies, but things happen in a much more incoherent fashion.”

What will be discussed this year?

The meeting’s website lists topics for discussion this year, including “China,” “Russia,” “Brexit” and “Climate Change and Sustainability.” One thing not listed, however, is the topic that is apparently driving Pompeo’s visit to Europe: Iran, which the Trump administration claims poses a growing threat.

Could the world’s power brokers end up discussing Iran anyway? Perhaps. But it’s unlikely that we’ll ever know.