Access wordpress blog in Symfony
Technically this does not depend on Symfony.
The first step of routing takes place at the level of the webservers (apache, nginx, symfony's inbuilt testing server).
These are configured to send every request made to the application to public/index.php.
From there Symfony picks up the request and determines what controller is to full-fill it.
If you would now go and tell the app to ignore the request it would need to forward it to the sub-folder which would likely result in undesired behaviour somewhere along the line.
So, since you want your sub-folder to be ignored you really want to set this rule before the request ever hits Symfony.
In other words - you should look at excluding the sub-folder from being passed to public/index.php at server level.
Here is an answer from way back that covers this for Apache using .htaccess - Symfony Ignore Directory in web/