I am a citizen of Eritrea and I work for the United Nations and have UN blue passport - UNLP, do I need an entrance visa to visit Greece as a tourist?
According to https://cibtvisas.com/forms?formname=portalforms/UNDP/Introduction%20-%20Guide-to-the-Issuance-of-UN-Travel-Documents.pdf Laissez-Passers are issued for use only on official travel during a period of employment. (K 36 Validity).
Timatic says you need a visa for Greece unless you are traveling on duty for a maximum stay of 90 days. https://www.timaticweb2.com/integration/external.php?ref=d975cfc59f5c0abd06d16e872198110b