Stupid Question But How Do I Get To Nightfall

just bought it today and want to play through with my prophecies guy but dunno who to speak to to get there

By the pier in LA is an NPC that'll give you the quest

Lionguard Figo atht esouthwest corner of lion's arch out on the dock

A more detailed answer:

First, you must have a merged account with both Prohecies and Nightfall.

Next, you need to perform a quest called "Sunspears in Kryta". The quest can be obtained from Lionguard Figo. During the quest you'll have to defend Lion's arch from a demonic invasion. Be sure to bring some higl level allies with you, as the demonic creatures are very high level and will mercilessly eat you alive.

Afterwards, you will be transferred to Elona. Don't forget to accept the quest rewards.

I've sucessfully henched it 3 times, even though A-net continually makes "improvements" to the quest so that it was different each time.

Last I tried, with a new mesmer, they actually lowered the level of the mobs quite a bit, but added more of them. Ironically, this made the quest harder to hench than when the monsters were level 28.

did it 3 times so far. First time, it was easy - my warrior, who had already finished both Prophecies and Factions was already lvl 20, so no trouble.

The other two times were more difficult. The characters were the first of their kind, and I wanted my heroes ASAP, so they were low level (low teens, IIRC) and had few skills available. Oh, and both had presearing collector armor... This was more trouble. I survived only because I had stronger guys in the party who helped me.