Gran Mountain is quite large, and you won't be able to explore all of it, especially the peaks, when you first arrive here. The only way that you can scale the mountain is by climbing up the established ropes. The highest door that you can reach on the west side of the mountain will only contain a hermit who informs you that you can't go any further east without a Crossbow.
In addition to the two enemies that you're already familiar with, you'll have to deal with a third new running enemy, the Phollorakos. They can be quite difficult to defeat at first, but the tougher ones will start to give you Tone and Last points which will help make you a lot stronger. As long as you've cast the Power Up spell, find a good spot, like up against one of the gray blocks, and destroy a bunch as they appear. Ideally, you should try to reach the first health increase so that you have four hit points before you enter Garloz.
Speaking of which, you will find the entrance to Garloz on the right side of the large gray block near the bottom. There are two doors along the far east side of the mountain that you can also visit. The highest one reports that the Tower of Garba can be found above you, but you don't have the power to access it just yet. The one below gives you an important tip: when you reach Garloz, first go west and then north. Head through the door to Garloz when you are ready.
Once you are equipped with the Wind Pulley and the Crossbow, you can explore much more of the higher regions of the mountain. The two previously unreachable doors on the west side offer life replenishing opportunities; the hermit behind the door high up in the tree will heal your wounds, and the hermit who lives in the highest peak will offer you a Life Potion if you possess the Coat of Arms and don't already have a potion.
You can then use the Crossbow to create new lines between the tree stumps found at the edge of various ledges and use the Wind Pulley to travel across the lines. Eventually, you will reach the Tower of Garba, a short but dangerous place that should be one of your later destinations as you get close to completing the game.