sneak in(to some place)
To enter some place in a quiet, sneaky, inconspicuous, or furtive manner. The burglar snuck in without making a sound. Marty came sneaking into the classroom, late as usual.
sneak in(to some place)
to enter a place quietly and in secret, perhaps without a ticket or permission. The kids tried to sneak into the rock concert, but they were stopped by the guards. Never try to sneak in. Sometimes they arrest you for trespassing.