The GR52a skirts the edge of the Mercantour National Park starting at Colmars (04 Alpes-de-Haute-Provence) in the valley of the Verdon, then heading east, south-east, and north-east to the Col de Tende (06 Alpes-Maritimes) in the corner of the French/Italian border. The FFRP Topoguide number 500 covers the GR52a and the GR510 under the title of Panoramique du Mercantour, rather a misnomer as the 52a studiously avoids crossing the National Park boundary, and the 510 hardly goes near it.

Details about route-finding at le Bioulet

The line of the GR52a shown on the IGN TOP25 map is accurate, but not all the buildings at le Bioulet are shown. As you approach le Bioulet, pass between two concrete pillars either side of the road. About 200m further, go up the private drive with "no entry" sign. There was no signpost nor a GR waymark at this point in April 2005. Continue in the same direction to reach a notice board / signpost (probably no. 285, but we didn't confirm this). Here you should pick up the waymarks again. The GR52a heads purposefully uphill in a north-easterly then northerly direction, and as shown on the map turns sharply south when it reaches the stream.

Do NOT take a lower WAYMARKED path which follows a more level route parallel to the road, heading north. The waymarks were bright and new in April 2005. This path does not turn back at the stream, but crosses it and continues to follow the direction of the road back towards St Martin, but higher up the hillside. It possibly connects with the dotted track shown ending at the large conduit.

We made the mistake of not passing the "no entry" sign and searched around in the woods for the path, eventually picking up the fresh waymarks of what turned out to be the lower path. We followed this over the stream and on for another few hundred metres before abandoning it and returning to le Bioulet, where we intersected with the correct path. We did not go as far as the notice board / signpost but could see it below us at the point where we found the right way.

The fresh white-and-red waymarks on the wrong path were confusing. We suspect that an alternative line for the GR52a is being or has been developed, possibly using the dotted track ending at the conduit. At the time of writing (May 2005) there is no mention of this on the FFRP website's mise à jour section.