1.

Many people are unaware of what has been achieved.

know

Many people do not know what has been achieved.

2.

Ten years ago the country park was nothing more than an idea.

only

Ten years ago the country park was only an idea.

3.

They settle down where it suits them.

feel

They settle down where they feel like it (feel comfortable / feel at ease).

4.

A good country park will be readily accessible.

reach

A good country park will be within easy reach.

5.

A good country park will be readily accessible for cars and pedestrians.

car / foot

A good country park will be readily accessible by car and on foot.