Slowly climbing up the valley form Nova Gorica you reach Kanal where Avče trails team made couple of amazing trails to ride. Plus they offer shuttle services. Reach them out at their FB web page There's a trail the the guide book from 2009 which was slightly modified in recent years to give you even more fun.
1300m of altitude difference, 10km of ascent, 13% of average slope, with 20% steepness on the very beginning of ascent just outside Zatolmin - these are some facts that make this way up to Sleme not very popular among mountain bike riders to say the least. But there are some who like it just for these facts. The way up takes some effort but when you get to the top where the highest mountain pasture of Tolmins region lies the view opens to the Julian alps on the East and West side. From here many possibilities for descent are available. The most popular is to go down to Mederje and via Pretovč straight down to Zatolmin. The single track is always empty and it allows a very high speed descent with some rocky sections just to keep the thing interesting.