The Thames Barrier, which has been in operation since 1983, is the largest and most expensive single element of London's flood-defence system.

Located at Woolwich and stretching a third of a mile across the Thames, it is a unique feat of engineering.

An information centre is open to visitors, featuring information boards to explain the story behind the construction of the barrier. It also has audio-visual presentations and working models which show how the barrier was built.

There is also a learning centre which is for school groups and offers environmental education packages for key stages 2 and 3.

There is a test closure of the Thames Barrier once a month for maintenance purposes.

On the other side of the river is the Thames Barrier Park, London's first new park in recent history. The park, with its fountains, playground and tea pavilion, is popular with families.

Information centre opening details: Seven days a week, October to March, 11am - 3pm; April to September, 10.30am - 4.30pm

Admission: Adults £1.50, children 75p, seniors £1

Tel: 020 8305 4188