That service has been (since around 2021–2022 intermittently, and more permanently since mid-2023 for many users). The original server was maintained by a Dutch hacker group, but it seems the telnet daemon is no longer running.
If you try:
telnet towel.blinkenlights.nl you’ll likely get a connection timeout or a refusal.
It looks like you’re referring to the classic that used to run via Telnet at towel.blinkenlights.nl .