What is this concrete lid in my alfresco area?

[ppp]

This is located in my alfresco. I can see the letters may be F T G S (and I S 100) not sure what that means!

I have an easement on my back yard if that has anything to do with this. 

[Jewelleryrescue]

Hi @ppp 

All places as  far as I know in modern times have there   concrete mushrooms to allow access to your sewer line on your  property for  clearing purposes and the like so dont make it disappear in a hurry.

I might be  wrong but a reasonable  guess.

[ppp]

Thanks mate!
Anyway, I'm not going to do anything with that. Just because I'm trying to improve drainage in my backyard and wanted to find out what is that. 

[EricL]

Hi @ppp 

That is an access cover for the sewage line in your area. Please do not cover it with permanent flooring or attempt to open it. 

If you need further assistance, please let us know.

Eric

[ppp]

Thank you @EricL