You can find the Razorfen Downs dungeon within Thousand Needles, Kalimdor.
The coordinates are (47.4,23.4)

Click for Dungeon Entrance:

Route:

Map 1

On the 1st boss to get the spider to come down use the Gong to the left.

Bosses:

1. Aarux

Quick Boss Tactics:
/i Get pulled in by Web Strand, run away. Inflicts nature damage to players.

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2. Mordresh Fire Eye

Quick Boss Tactics:
/i Kill groups of skeletons. Interrupt Lava Burst. Boss summons fire mobs Blazing Servitors. Avoid fire balls falling around them. They create lines of fire between themselves, avoid these.

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3. Mushlump

Quick Boss Tactics:
/i Smack Down hits current target dealing physical damage. Avoid frontal cone Tummy Ache, vomiting a line of green. Vomits a cloud of disease on floor, move away.

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4. Death Speaker Blackthorn

Quick Boss Tactics:
/i Move out of frontal cone Shock Wave. Summons mobs Splinterbone Warriors. They interrupt spell casting & use knock backs. Interrupt Searing Shadows & Shadowmend.

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5. Amnennar the Coldbringer

Quick Boss Tactics:
/i Stand in the Redeemed Soil (green circles) on floor to remove Soul Leech. These circles also heal you. Move away from frost balls Frozen Bomb.