Simplify the following text for a Grade 3 native English-speaking person.
Original: It is a narrow sweep of land between 20 and 400 metres wide , encircling a large lagoon 18 km long and 14 km wide , with a surface of 275 kmÂ , by far the largest lagoon in Tuvalu .
Simplified: It is a narrow sweep of land between 20 and 400 meters wide .