Royal Botanic Gardens, Kew

The one on every postcard, and the one to do first if you only have half a day. It is a rainforest under curved Victorian glass, humid enough that your camera lens will fog on the way in, and dense enough that you lose sight of the doors within about thirty seconds.

Give it thirty to forty minutes minimum. People who allow ten end up walking through it like a corridor, which rather misses the point. Most people do one loop at ground level and leave, which is part of why it feels busier than it is.

The largest Victorian glasshouse in the world, covering nearly two acres, and restored back into use after years under scaffolding. Cooler and calmer than the Palm House, and I think the better building, though I appear to be in a minority on that. Give it another half hour or so. The plants here are the ones that would not survive a British winter outdoors but do not want tropical heat either, which sounds unpromising and produces some of the strangest specimens on site.

Ten climate zones under one roof, desert through to rainforest, arranged so you walk out of one and straight into the next. It is the most compressed thing at Kew. Twenty minutes here covers more botanical ground than an hour outside does. The obvious refuge on a wet day, which of course means everyone else has had the same thought, so do it first thing rather than at two in the afternoon.

Two hundred metres of walkway, eighteen metres up, threading through the woodland canopy. It sways slightly, which is either the appeal or the problem depending on who you came with.

Two practical things. It shuts at 6pm even on the long summer evenings when the Gardens stay open until eight, and it sits a fair walk from the main gates, so it is a poor thing to save until your legs have gone.

The Waterlily House is small, hot and completely worth the detour for the giant lily pads. The sort of place you plan to glance at for two minutes and then stand in for fifteen.

The Marianne North Gallery nearby is the odd and brilliant one, floor to ceiling with her paintings, hung edge to edge in a way no modern curator would get away with. The Shirley Sherwood Gallery of Botanical Art rotates its shows. Both close at 5.30pm, and both are a good place to sit down when your legs have gone.

Not the obvious recommendation, but the honest one for a first visit. Kew is much bigger than the map makes it look, and the train gives you the shape of the place before you commit your legs to a direction. Regular visitors will tell you to walk it and they are right eventually, but on day one twenty minutes on the train saves you an hour of going the wrong way.