What year did Switzerland join the United Nations?

2002 → nose · sun.

Guarding its neutrality, Switzerland stayed out of the United Nations for decades — hosting the UN's European headquarters in Geneva yet sitting only as an observer — until a 2002 referendum narrowly approved membership (about 55% in favour). It thereby became the first country ever to join the UN by a direct popular vote of its citizens. Peg 20 · 02 → nose · sun: a nose sniffing the sun.

Go deeper:

• Swiss Voters Approve UN Membership, 2002 — AP Archive — contemporaneous news footage of the referendum.
• 2002 Swiss referendums — Wikipedia — the March 2002 vote (54.6% yes) that took Switzerland into the UN.