You must reach at least Honored reputation with the Argent Dawn to begin the attunement quest "The Dread Citadel - Naxxramas".
Consider utilizing community-created addon packs for easier navigation and preparation. Key Encounters and Tips XXSu.eh.ai.naXX.zip
The quest is completed by speaking to Archmage Angela Dosantos at Light's Hope Chapel in the Eastern Plaguelands. You must reach at least Honored reputation with
Naxxramas was historically a 40-man raid, requiring high coordination. XXSu.eh.ai.naXX.zip
The cost to enter decreases at higher reputations, starting at 60 gold at Honored and becoming free at Exalted. Preparation and Consumables
For bosses like Sapphiron, melee DPS and tanks should aim for roughly 150 frost resistance, while healers and ranged DPS should have around 100 (unbuffed).