Gwaith-i-Erynthin Building ???

[cmdrnarrain]

Gwaith-i-Erynthin

What the heck is it and do Silvan Elves need to build it?

[tugaguy]

King Kong wrote this answer on a different post about this building:

These seemingly "needless" buildings for the high and silvan elves are part of the elven gameplay and will help you a lot to get certain Guilds, which on the other hand will allow for more population growth.
Just look at the description of the Dance or History guilds and you will see what buildings you need to get them.
These "needless" buildings represent some way of life for the elves: not everything must have advantages for money or military. If you don't build them you will have to wait very long until you get higher city levels.

The population bonus for the AI just kicks in a bit earlier since it won't accept enough guilds to have a proper population growth. These buildings have also nothing to do with this elven reforge thing.

[Wizad]

If you build it, then you are able to receive a guild offer from the Dance Guild. The Dance Guild gives 0.5% population growth.

[Lortano]

If you build it, then you are able to receive a guild offer from the Dance Guild. The Dance Guild gives 0.5% population growth.

And considering that pop growth is rather low in Tatw, that extra boost could be several turns difference for getting elite troops out fast from a fully upgraded city, or getting Forest Wardens from a backwater.

A very useful building indeed.

[Aikanár]

The original concept of the Gardeners Guild (Gwaith-i-Erynthin) was to simulate sort of an silvan elven lifestyle concerned with celebrating nature, harvest and healing therewith providing benefits in pop growth, happyness and reduction of squalor. It also was a prerequisite to build the Enthouse. It was not, however, a prerequisite for the Gwaith-i-Glinadir'a'mereth which is the Dancers and Singers Guild.
As what it ended up in the official release, I've no clue.