The Security Gateway directory where an administrator can find VPN debug log files generated during Site-to-Site VPN troubleshooting is $FWDIR/log/. The $FWDIR environment variable usually points to the installation directory of Check Point FireWall-1, and it contains various subdirectories for logs, configurations, and other important files. The log files related to VPN activities are stored in the $FWDIR/log/ directory.