Tate Modern is scary

The spider is back, but this time it's lurking outside. The conversion of Bankside power station complete, Tate Modern finally opened its vast doors to the public in 2001. Inside was installed Maman, the spider, a giant steel structure by Louise Bourgeois.

I wrote in a newspaper column at the time: "it is doubtful any state-of-the-art structure could have been more suitable for a museum of modern art than the austere, art-deco influenced building at Bankside. To begin with, economics would never have permitted such a vast Galleria as the Turbine Hall to be included in the specification of a purpose built gallery…

The most stunning area is undoubtedly the Turbine Hall. Here Louise Bourgeois' giant sculptures suit the scale of the space. Thirty foot towers with stairways and looking glasses are interactive pieces that mirror the industrial style of the building.

Next to them lurks a monster spider sculpture – this awe inspiring piece is almost an Alice in Wonderland experience. The spider looks down – as visitors do from the galleried mezzanines above – on Gulliver-sized figures.

Surreal: giant spider, miniature people; one's perception of the real world turned on its head. The juxtaposition of its organic, natural form with the rigidity of the powerful man-made building is equally interesting."

A large retrospective of Bourgeois' work has just opened at Tate Modern. The large show is chronological and traces her work of decades – she is now 95 – from painting, to geometric sculptures onto organic pieces in a variety of materials.

She admired Giacometti, liked Bacon's work, knew Duchamp and Brancusi and was a pupil of Leger: there are few artists alive today who could claim that lot. And she is still imaginative and still exorcising childhood demons in her work.

Bourgeois' pieces are not for the faint hearted: when in the turbine hall her dark, giant arachnid stood on its enormous jointed legs guarding a pile of its marble eggs. The observer could feel the menace, the fierce protectiveness of a mother.

You may be able to plumb the depths of the artist's psyche better than me but I must admit I wasn't too taken with what I thought I could see there. A secure and happy place it did not seem to be but perhaps a little angst is what great artists all need. I suspect that children will think of Maman as pure Disney and teenagers as computer graphic and not be as affected as some of us more pathetic souls.

The giant spider now stands outside Tate Modern and if you suffer nightmares or don't like horror movies, you'll know right away that it's not the place or the show for you. And it seems that this could apply if you venture inside too: Doris Salcedo – a Colombian artist - has a new installation there called Shibboleth. It's a 167m long fissure that zigzags across the floor of the Tate and it widens to such an extent that visitors could fall down if not alert.

Like an earthquake Shibboleth rents a landscape in two: Salcedo sets out to show the conflicts that divide us whether of thought, politics, immigration or art. Is it a crack or a scar, a negative space or two spaces, a chasm that is ripping our society apart or what exactly?

I haven't been to the show yet but I must, it sounds so thought provoking. And I have a feeling that it will be as impressive as that giant spider - the one that's lurking outside – but I hope not as scary.