diff --git a/grid/factory/GridImportance.h b/grid/factory/GridImportance.h
index 34d39a5..8ab6473 100644
--- a/grid/factory/GridImportance.h
+++ b/grid/factory/GridImportance.h
@@ -40,6 +40,9 @@ public:
 		GridFactory<T> fac(inv);
 		fac.addInverted(g, z_cm);
 
+		// sanity check
+		Assert::isFalse(inv.getNumNodes() == 0, "inverted grid is empty!");
+
 		// construct KNN search
 		KNN<Grid<T>, 3> knn(inv);
 
@@ -194,7 +197,7 @@ public:
 	float getWallImportance(float dist_m) {
 
 		// avoid sticking too close to walls (unlikely)
-		static Distribution::Normal<float> avoidWalls(0.0, 0.4);
+		static Distribution::Normal<float> avoidWalls(0.0, 0.5);
 
 		// favour walking near walls (likely)
 		static Distribution::Normal<float> stickToWalls(0.9, 0.5);
diff --git a/grid/walk/GridWalkLightAtTheEndOfTheTunnel.h b/grid/walk/GridWalkLightAtTheEndOfTheTunnel.h
index 45ea259..d5b4815 100644
--- a/grid/walk/GridWalkLightAtTheEndOfTheTunnel.h
+++ b/grid/walk/GridWalkLightAtTheEndOfTheTunnel.h
@@ -155,11 +155,14 @@ private:
 		// update the heading-change and walked-distance
 		next.headingChange_rad += next.heading.getRAD() - cur.heading.getRAD();
 		next.distanceWalked_m += walked_m;
+		++((T*)next.node)->cnt;		// TODO: eval only
 
 		if (next.node->z_cm != cur.node->z_cm) {
 			int i = 0;
 		}
 
+
+
 		// done?
 		if (distRest_m <= 0) {return next;}
 
diff --git a/grid/walk/GridWalkSimpleControl.h b/grid/walk/GridWalkSimpleControl.h
index 82f0c6e..636646f 100644
--- a/grid/walk/GridWalkSimpleControl.h
+++ b/grid/walk/GridWalkSimpleControl.h
@@ -114,7 +114,7 @@ private:
 			if (drawer.getCumProbability() < 0.1 && (--retries) >= 0) {
 				walked_m = 0;
 				cur = start;
-				WHAT THE HELL
+				//WHAT THE HELL
 				if (retries == 0) { reqHeading = dChange.draw(); }
 				continue;
 			}
diff --git a/nav/dijkstra/Dijkstra.h b/nav/dijkstra/Dijkstra.h
index 9a79cc7..0180643 100644
--- a/nav/dijkstra/Dijkstra.h
+++ b/nav/dijkstra/Dijkstra.h
@@ -22,9 +22,10 @@ template <typename T> class Dijkstra {
 
 public:
 
-	/** get the dijkstra-pendant for the given user-node */
-	DijkstraNode<T>* getNode(const T& userNode) {
-		return nodes[&userNode];
+	/** get the dijkstra-pendant for the given user-node. null if none matches */
+	DijkstraNode<T>* getNode(const T& userNode) const {
+		auto it = nodes.find(&userNode);
+		return (unlikely(it == nodes.end())) ? (nullptr) : (it->second);
 	}
 
 	/** build shortest path from start to end using the provided wrapper-class */
diff --git a/nav/dijkstra/DijkstraPath.h b/nav/dijkstra/DijkstraPath.h
index 76ef80f..fbcb34f 100644
--- a/nav/dijkstra/DijkstraPath.h
+++ b/nav/dijkstra/DijkstraPath.h
@@ -2,6 +2,9 @@
 #define DIJKSTRAPATH_H
 
 #include "DijkstraStructs.h"
+#include <vector>
+
+#include "../../Assertions.h"
 
 /**
  * describes a dijkstra-generated path between end and start.
@@ -20,15 +23,30 @@ public:
 	/** ctor from end- to start-node */
 	DijkstraPath(DijkstraNode<T>* end, DijkstraNode<T>* start) {
 
+		// sanity checks
+		Assert::isNotNull(end, "end-node must not be null");
+		Assert::isNotNull(start, "start-node must not be null");
+
 		// follow the path from the end to the start
 		DijkstraNode<T>* curNode = end;
 		while (curNode != start) {
+
+			// sanity check in case no path between start and end exists
+			Assert::isNotNull(curNode, "there is not path between start and end. did you accidentially swap start and end?");
+
+			// append
 			path.push_back(curNode);
 			curNode = curNode->previous;
+
 		}
 
 	}
 
+	/** allow iteration */
+	decltype(path.begin()) begin()	{return path.begin();}
+	decltype(path.end()) end()		{return path.end();}
+
+
 	/** NANOFLANN: number of elements in the path */
 	inline int kdtree_get_point_count() const {
 		return path.size();