While summer in Death Valley is not to be taken lightly, we did venture in the mornings and evenings when the sun was not as strong (temps still in 118 F range.) Mosaic Canyon was beautiful and shaded when we went (2.4 mile gravel road to trail head) and we couldn't miss a quick trip to Badwater, the lowest elevation spot in the U.S., where people had fried eggs on the pavement. (The hot, dry wind there necessitates carrying drinking water at all times.) We would also recommend Artist's Scenic Drive, a 9 mile, one-way trip though the pigmented bluffs that make up the canyon walls as another great summer activity (one that you can do from inside the air conditioned car. ) Really beautiful, like Badlands NP in South Dakota. We'll have to come back in winter or spring for more exploring and longer hikes.