un.org seems to be up and working at the moment with no reported errors.ping:
No one seems to have reported problems with un.org within the past 24hours. If you can't reach it you can help others know below or by writing a comment to describe your problems.
If un.org doesn't have any reported problems, and seems to be up, you can troubleshoot common problems that you might be facing.
Try opening un.org in another browser than the one you're using.
See browsehappy.com for a list of good browsers
Some ISPs (Internet Service Provider) block sites like un.org due to various reasons. You can try accessing the page by surfing through a VPN (Virtual Private Network).