Can I cross a mountain range without leaving 420m above sea level?

You know those curvy orange lines on the map that indicate altitude and steepness? Well what if I tried to follow one? My map tells me I'm going to be passing over farmland, ravines as I straddle the feet of big Welsh mountains, but will the terrain and foliage allow me to stay at the same altitude (420m above sea level) the entire time without any injuries? NEW ALBUM: -Buy on Bandcamp: https://flopsysdream.bandcamp.com/album/pleasant-pudding -Order Vinyl: https://cargorecordsdirect.co.uk/products/flopsy-s-dream-pleasant-pudding?srsltid=AfmBOopBctr9P9pKTzTQRcfUBfehoy3VYo1lyVNdHvbb4BbV2F0P-1Tm (Streaming + YouTube links coming soon)