Here you go:
- Austria: http://www.amap.at
- France: http://www.geoportail.gouv.fr
- Germany, Bavaria: http://geoportal.bayern.de/bayernatlas (check box "Wanderwege")
- Italy: http://www.pcn.minambiente.it/viewer
- Switzerland: http://map.schweizmobil.ch (check boxes in "Wanderland")
- World: http://opentopomap.org