One can access the logs via an SSH session to the server.
The logs of any given web node are located on that web node itself in /var/log/sites/[site].[env]/logs/[servername].
The following types of logs are available:
Apache access log — access.log
Apache error log — error.log
Drupal page request log — drupal-requests.log
Drupal watchdog — drupal-watchdog.log
PHP error log — php-errors.log