The best replacement for slopes is hills.

The best alternatives to slopes are rated as following:
★★★★★  hills
★★★  cliffs
★★  south facing slopes
★  paoli peaks
★  angles

Your alternative for slopes is not listed? Suggest!
Speaking about slopes, one probably shouldn't forget about graphs.

Other search terms related to slopes and their ratings are:
★★★★★ graphs
★★★ lines
★★★ perpendicular lines
You have in mind a companion for slopes and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of slopes in all years. Click on graph for more.
slopes
hills
cliffs