Boulder

The Flatirons - five slabs of tilted sandstone standing against the foothills - are the backdrop to everything here, and the reason they are still undeveloped is a decision: in 1967 Boulder voters approved a dedicated sales tax to buy open space around the city, and the resulting greenbelt now surrounds it and caps growth, with a 1972 height limit keeping the mountain views. Pearl Street's four blocks were pedestrianised in 1977 and function as the centre, with street performers. The University of Colorado is here, along with NIST, NOAA and NCAR - the last in a Pei building on a mesa above town, open to visitors with an exhibit floor.

What to look for

• The Flatirons - tilted sandstone slabs above the city.
• A greenbelt bought by referendum - with a sales tax voters approved in 1967.
• Pearl Street Mall - pedestrianised since 1977.
• NCAR's Pei building - on the mesa, with a public exhibit floor.

When to go

May to October; trails are busy at weekends. A full day.

Practical notes

Trailhead parking fills early and some sites charge non-residents. Altitude at 1,650 metres affects arrivals from sea level. It is expensive. Wildfire seasons have closed foothill trails.

Nearby

Rocky Mountain National Park is north-west; Denver is south-east.

Key facts