If it is not the boot device, it will only throw an error trying to mount it. But that slows the boot process down and gets old real quick. To use a custom mount point use:
sudo cryptsetup luksOpen /dev/sda1 my_encrypted_volume

Now you can mount it as usual:

sudo mkdir /media/my_device
sudo mount /dev/mapper/my_encrypted_volume /media/my_device

To lock the container again, it needs to be unmounted first:

sudo umount /media/my_device
sudo cryptsetup luksClose my_encrypted_volume