Excursion
Most of the excursions recommended below start from Chamonix. So you first need to go to Chamonix. This can be done by train or by bus (basically one bus per hour). The bus is recommended because the bus stop is in the center of Les Houches and is much closer than the train station. For hiking, all the trails below are in a very good state and can be hiked with normal hiking shoes or tennis shoes. Beware of the snow. Normally at this time of the year there is no snow on these trails, but there can be exceptions.
The most spectacular: Aiguille du Midi

A cable car brings you to Aiguille du Midi from downtown Chamonix. It requires booking in advance. The cost is between 60€ and 80€.
If the weather is not too windy you can cross the Vallée Blanche to Helbronner.

The second most spectacular: Montenvers and Vallée blanche

Opens in May 23. A train brings you to Montenvers for a gorgeous view of the "mer de glace" (one of the biggest glaciers in the Alps, unfortunately heavily damaged by the global warming). You can even hike down to the glacier. You do not need a reservation but you need a ticket (41€): more information here.