C'est Yaevinn qui donne la quête Echos d'hier à Geralt au début du Chapitre III, si le sorceleur le trouve dans le bosquet des druides dans les marais. L'elfe demande à Geralt d'aller trouver ces confrères qui sont disparus dans les égouts du Quartier des marchands.
Guide
Find Yaevinn in the swamp and get the quest, then proceed to the Quartier des marchands (maison de Triss) using the téléportateur in the tour du mage. From there, head to the sewers.
After killing the ten or so drowners en route, you will find a dwarf named Ren Grouver and two elves standing around having a conversation about a skirmish. Talk to Ren. He'll tell you about their most recent encounter with a monster in the elven ruins and ask you to get rid it. The beast is not only blocking his path and but has killed some of his compatriots. He describes one of the unfortunate as having simply "exploded".
Take the mission and proceed into the ruins through the tunnel which can be seen through a large opening in the sewer wall. When you arrive at your final destination, you should see a cut scene featuring a succubus-like creature. Enter the room and kill it - it's a brouxe (vampire).
When you're done, Ren will enter the hall and thank you for your help. At this point Geralt mentions that the fight was "worth more than [Ren could possibly] know", which is strange as the actual battle is a breeze, but I digress. Next, Yaevinn arrives via the Elven Ruins téléportateur, thanks you, tells you to forget what you've just seen here and gives you your reward. That's it, all done.
Notes
- voir aussi la traduction du guide « Gamepressure »
- If you have completed « La réception huppée » first, this quest and « Six pieds sous terre » are mutually exclusive. If you finish « La réception huppée » and « Six pieds sous terre », if you try to make your way anywhere at all, a child will stop you and give to you the « Les héros de Yaevinn » quest. The relationship between « La réception huppée », « Six pieds sous terre » and this quest may be tied to the « Identité » quest and talking to Thaler during « La réception huppée », so if the dialogue line about Geralt's motivations is not pursued, it may postpone the event trigger. That has not been tested, however. See the « Les héros de Yaevinn » quest for more details on the relationships between these quests.
- Even if you ignore the child and go to the Swamp anyway, you will still find Yaevinn but he will not give you the quest because narratively he is really at the Banque Vivaldi in the basement.
- It is advisable to do the first few quests in Act III in the following order:
- « Six pieds sous terre » for Siegfried, then
- this quest for Yaevinn, then
- you could sneak in Le luth de Jaskier here, and every other quest in Act III with the exception of the two below, « La belle et la bête », and anything involving Velerad.
- « La réception huppée », and finally
- « Les héros de Yaevinn »
- If you fail (failure is such a harsh way to put it!) to get the Echoes of Yesterday quest, it is not the end of the world, or even of consequence to the game narrative particularly. You will lose the 6500 quest XP and the XP for killing the brouxe, but with some work these XP can be made up by killing the endless supply of alps also found in the ruines. The Alps are present before this quest and « Les héros de Yaevinn », but do not appear again until you have visited the bank again after completing « Les héros de Yaevinn ». This seems to reset the spawning of the Alps. The Elven Ruins teleporter will not be immediately activated after this quest, but it does get activated after completing « Les héros de Yaevinn ».
- Upon accepting the quest from Yaevinn in the bosquet des druides, he'll tell you a story about Lara Dorren and mention Feainnewedd now grows where she "breathed her last." This conversation does not unlock Feainnewedd in the journal.
- Completing this quest causes the forgernon nain to start doing business with Geralt
- Completing this quest causes the Armurier de l'Ordre to stop doing business with Geralt
Phases
The Elven Temple
Yaevinn asked me to find his men. Apparently, they descended into the sewers to find an old elven temple. He also asked me to recover all the artefacts related to Lara I can find. Yaevinn asked me to find his men in the sewers of Vizima.
Evil
I met Yaevinn's men. Just as he said, they tried to get inside the temple, but found something living there, something evil and powerful. Only two elves and one dwarf survived. I should find out what happened to the others. I should find out what killed Yaevinn's men.
The Vampire
La brouxe qui cause tout le vacarme
The temple was home to a vampire, one powerful enough to kill most of Yaevinn's men. It was a tough fight, but I slew him. (editorial -- oh really? and wasn't it a her?) The elf should reward me generously. I slew the vampire who killed Yaevinn's men. The elf should reward me generously. (2000 XP)
Yaevinn
Although I found no mementos, Grouver thanked me. It's all very strange... Why did the Scoia'tael need to get to the elven ruins? Grouver also said Yaevinn would pay me for completing the job. We found no artefacts. Why did the Scoia'tael want to get to the elven ruins? I need to speak with Yaevinn.
Elven Ruins
I sense Yaevinn hasn't told me something. Why did he want to get to the elven ruins so badly? There's nothing here... I brought Yaevinn to the elven ruins. (300 
+ 4500 XP)