Simplify the following text for a Grade 12 native English-speaking person.
Original: The complex was protected by approximately four metres of concrete , and about 30 small rooms were distributed over two levels with exits into the main buildings and an emergency exit into the gardens .
Simplified: The complex was protected by circa four meters of concrete , and about 30 small rooms were distributed over two levels with exits into the main buildings and an emergency exit into the garden .