Cove Park, Scotland
Essentially a sophisticated artists' retreat, Cove Park was founded in 1999 on Scotland's Rosneath peninsula. While creative types come to be inspired, or to take part in events, the accommodation is also open to the public. Guests can choose between two oak Pods – originally used on the BBC's first Castaway programme and now furnished smartly by Habitat – or book into one of six ex-shipping container Cubes.
Cove Park, Peaton Hill, Cove, Argyll and Bute, Scotland (01436 850123; www.covepark.org). Pods start at £100 and Cubes at £40, room only; minimum two-night stay.
ElquiDomos' six geodesic domes are all about location. Not because this part of northern Chile is particularly picturesque, but because the skies are famously clear year-round. ElquiDomos sells itself as the first "astrohotel" in the southern hemisphere. Owned by Esteban Zarate, a former regional director of the Chilean tourist board, each dome has a living room and bathroom on the ground floor and a bedroom up above (with telescopes and detachable roofs so that dedicated stargazers can watch the skies from bed). Astronomic tours and night-time horse rides can also be arranged.
ElquiDomos, just outside Pisco Elqui, east of La Serena, Coquimbo Region, Chile (00 56 51 211 453; www.elquidomos.cl). Domes start at CLP 45,000 (£44), room only.
Das Park, Austria
Open from May to October, Das Park is a set of three concrete drain pipes reconfigured as bedrooms and let out over the internet (when you book you get a door code that allows access during your stay). Designed by artist Andreas Strauss, they are more comfortable than they sound, with a double bed, storage, light, a blanket and a cotton sleeping bag. Fortunately for any guests worried about claustrophobia, they're also tall enough to stand up in. The catch? Don't expect en suite facilities – guests use public toilets, showers, a bar and café in the surrounding park.
Das Park, Ottensheim, near Linz, Austria ( www.dasparkhotel.net). The pipes/ pods are let on an honesty basis; you leave as much as you think is fair.
Free Spirit Spheres, Canada
Like overgrown birds' nests suspended high in the tree canopy, these two wooden spheres are strung up in a forest on Vancouver Island, close to a park with a network of underground caves, swimming holes and opportunities for hiking and mountain biking. The spheres are strong but dynamic. If you get a fierce wind, or someone rolls around in bed, expect some swaying. You'll probably want to go to the loo before you climb under the covers, too, since the shared bathroom is 60 metres away.
Free Spirit Spheres, 420 Horne Lake Road, Qualicum Beach, Vancouver Island, British Columbia, Canada (001 250 757 9445; www.freespiritspheres.com). Eryn, the larger sphere, starts at C$150 (£68) while Eve costs C$100 (£45), room only.
Yabyum Resort, India
Set on the quieter far north coast of Goa, on the outskirts of a fishing village, Yabyum is your quintessential tropical retreat (it closes during the monsoon). In one direction is a beach of soft fawn-coloured sand, in the other shady coconut and banana plantations. The only break from the norm is the accommodation. While there are more conventional cottages available, the resort also features dome bedrooms made from rock, palm leaves and mango wood. Other facilities include an in-house masseur/reiki practitioner.
Yabyum Resort, Ashvem, Goa, India (00 91 832 651 0392; www.yabyumresorts.com). Pods start at Rs4,000 (£49), including an organic breakfast.